Traffic and Environmental Management

CHAPTER 5

Traffic and Environmental Management TRAFFIC MANAGEMENT

The principal aim of traffic management is to maximise the use of the existing street system and improve road safety, without impairing environmental quality. It is analogous to work study and production control in industry and is most appropriately applied to short-term and low capital cost improvements, thus improving, in economic terms, the supply. Management measures may relate to a single traffic category, such as pedestrians, or to mixed traffic and the close operational control of feeder routes to urban motorways. Most forms of traffic regulation produce some disadvantages which must be more than offset by the advantages gained. These disadvantages, e.g. to motorists, may well be related to the improvement of public transport services, to pedestrian­ ised facilities for shoppers, or to longer times being set on a pedestrian signal to allow elderly or disabled people to cross a road without hurrying. The definition of a study area will not only include a particular length of facility but also adjacent parts that may be affected, e.g. servicing frontages, rescheduling bus routes and stops, adjusting signals, erecting signs and signals on intersecting streets, etc. Detailed inventories are prepared of existing layouts, control devices, street furniture, adjacent land uses, environmental factors and traffic flows, delays and speeds. If accurate economic assessments are needed, some origin and destination 210

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211

information is necessary, particularly where traffic will be rerouted or diverted. Alternative schemes are prepared and evaluated, and it may be necessary to try out parts of the scheme before final implementation. The aims and objectives of the proposals must be widely disseminated to the affected public through the media, and at public meetings. Traffic management may entail alterations to the geometric layout, provision of additional guidance and control devices such as bollards, signs, signals, pedestrian guard rails, pedestrian crossings and lighting. Standing vehicles may also require the construction of ancillary pave­ ment areas, such as bus draw-ins and loading and unloading bays for commercial vehicles. Moving traffic is assisted by the coordination of traffic signals, adjustments to controllers and reducing conflicts by the use of one-way streets, reversible flow lanes for roads with directional flow peaks, and the limitation of selected turning movements at intersections.

ONE-WAY STREETS Land uses are usually serviced by traffic approaching from all direc­ tions and thus, when designing one-way schemes, complementary streets are required with suitable frequencies of interconnecting streets. Grid-iron layouts are ideal, as they allow paired streets with similar capacities. Terminal points of one-way streets are critical areas needing careful design of the resulting conflict points imposed by the demands of additional turning traffic. At sites with high flows, one-way working of the cross streets is advantageous. Elongated systems, with a separa­ tion of less than 500 m between street pairs, reduces the likely journey kilometres run on the network. Reversible one-way systems can partially overcome capacity limitations of a network but need complex, purposedesigned signs to display appropriate messages and automatic switching of control devices. Special arrangements can be made for buses to minimise walking distances to passengers by constructing counter-flow bus lanes where there are suitable street widths. The principal advant­ ages and disadvantages of one-way systems are set out in Table 5.1. The major costs of one-way systems lie in the provision of traffic signs, which are comparatively inexpensive compared to new road

212

Traffic Planning and Engineering

construction, and some of the savings can be allocated to the improve­ ment of junctions and the provision of more complex signalisation. By increasing capacity one-way streets often allow a continuation of metered parking, which may be essential to the life of an area. Finally, besides providing signs, careful road markings and the channelisation of junctions to prevent incorrect movement are always essential. However, greater visual intrusion generally results from one-way schemes, and higher traffic speeds tend to exacerbate community severance by creating greater difficulties in crossing the street, isolating one side from the other. TABLE 5.1. Advantages and Disadvantages of One-way Streets Advantages

Disadvantages

(i) Potential increase in capacity at and (0 Longer journey distances and in­ between junctions and possible im­ creased traffic volume on parts of the network leading to more turning provements in traffic distribution traffic at end points (ii) Fewer pedestrian and vehicle con­ (ii) Difficulty of routeing traffic through an area, particularly for strangers. flicts, generally reducing accident Loss of amenity for residents in areas rates and eliminating severe headof one-way streets and possible en­ on collisions vironmental deterioration (iii) Improved kerb parking conditions (iii) Diversion of public transport loading and less interference from bus stops, points and affects on bus scheduling and loading and unloading vehicles and route coverage (iv) Improved utilisation of streets with (iv) Increased walking distances for public transport passengers odd numbers of lanes (v) Easier application of progressive (v) Opposition from commercial in­ terests along one-way routes systems of traffic signal control (vi) Better connections to and from (vi) Difficulties of driver and pedestrian ramps at urban motorway inter­ familiarisation during initial phases changes and simplification of traffic of scheme distribution to the local street system

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213

TRAFFIC STUDIES IN MANAGEMENT Full traffic studies are required before taking management decisions, and this is particularly the case in considering one-way systems. Inven­ tories must be compiled of the layout, siting of existing signs, signals, pedestrian crossings and the land use of frontages. Volumetric classified counts must be taken throughout the area by hour and direction, together with the types and numbers of turning movements at inter­ sections. Speed and delay measurements are also required, and also data on parking characteristics. Finally, information is required on the total movements of pedestrians, including those to and from public transport stops, and the routes and frequency of services. The area study results will allow the theoretical assignment of traffic to the possible alternative one-way routes and these can be evaluated with new capacity computations. Unidirectional volumes and journey speed are then estimated and compared with existing speeds. By making due allowance for increased journey distance it is possible to select the most advantageous scheme. The new one-way streets must allow for rerouted bus services and the changes in pedestrian movement. Sub­ sidiary investigations into accidents on the existing and proposed net­ work will also influence choices. Commercial interests have to be convinced of the wisdom of the measures if severe opposition and delay to a scheme are to be prevented. As one-way streets are only one method of increasing traffic flow and reducing delay, other measures, such as parking and unloading restric­ tions and progressive signal systems, should be considered at the same time. Compromise will often be necessary, and some or all of the above improvements may be included in a phased programme. Once all these types of measures have been effected, new road construction becomes inevitable if further capacity is needed. If serious traffic dislocation is to be avoided in the future, adequate planning and execution of new work must be made before the final restriction is operated. The general application of one-way street principles is more difficult to achieve in British cities than in many countries because of basic differences in street layout. However, sensibly applied, these measures result in higher flows, improvements in safety, and often there will be decreases in journey time due to higher running speeds. Flow conditions

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Traffic Planning and Engineering

are normally more stable and less subject to breakdown. Figure 5.1 shows a number of applications of one-way street systems.

¥ *!♦

M — Λ

It

Cross-streets one-way (no interlocking turns)

Original layout

^μ—

^

i

ft

' Environmental area

r ., Environmental f area

Cross-streets two-way

Cross-streets terminated

F I G . 5.1. One-way street systems.

Assignment in Traffic Management A problem resulting from traffic management schemes is the need to estimate the effects of traffic redistribution on the network, not only to judge the efficacy of a scheme but to reveal its side effects. An assign­ ment model CONTRAM suitable for such purposes is being developed by the TRRL for motorway control strategies. Its main function is to reassign traffic subject to changes in conditions. Vehicles are processed in batches of 20 (packets) having the same origin and destination and reach destinations by routes according to the prevailing conditions (given the link undelayed running times, delays due to flows exceeding capacity and junction controls) in the shortest time. Iteration is used to simulate the effects of departure times on the interaction of packages affecting the "best" routes in the network. It is also appropriate to consider environmental impacts in the assignment process. Such aspects as visual intrusion, barrier effects (the routeing of desire line movements across new facilities by comparison with previous distributions by mode of crossing opportunities and any

Traffic and Environmental Management

215

subsequent limitations of them), the noise climate induced by the resultant traffic flows, mean speeds of flows, and proportions of heavy goods vehicles and points of entry or exit along the routes. Costs of earth mounding and barrier construction can also be taken into account given the relative elevations of source and receiver. Examination of the total network position can suggest rerouteing opportunities for traffic to alleviate environmentally weak areas of design. Further detailed study of sensitive areas can highlight property eligible for compensation due to the improvements or new works, and its aggregate cost. Turning Traffic and Clearways Each turning vehicle at a junction imposes an additional delay, over and above that of a through vehicle, varying from zero for a diverging vehicle leaving a route at a speed equal to that of through vehicles, to a value tending to infinity for a right-turning vehicle, causing a lock-up of the junction. The limitation of capacity and the reduction of total delay from these causes is controlled by banning, completely or partially, selected turning movements. It must be borne in mind, however, that delay may be incurred additionally when the turning movement is made in several stages and it must be shown that the aggregate overall delay for all vehicles is minimised. Exit left turns are dealt with by ensuring adequate radii for the class and speed of traffic. Right turns across traffic streams can be replaced by T-, G-, and Q-turns as illustrated in Fig. 5.2. With most traffic management schemes, certain vehicles, such as public transport, can be given favoured treatment by permitting turns banned to the other vehicles or other operating advantages. Whereas clearways were first introduced on rural roads mainly to enhance safety, they now have important traffic management advantages on urban roads. The principal objective is to improve traffic flow by restricting waiting and loading. While rural routes do not require road markings, and usually only the provision of occasional laybys, those in urban areas generally restrict the control to specified peak periods and need extensive signing and enforcement. Pedestrian accidents have been reduced by up to a half and traffic flows improved by up to 10% on roads without previous controls. While no benefits are gained at junc­ tions their use enables signal progression schemes to be instituted.

216

Traffic Planning and Engineering

=5fr G-Turn

T-Turn "*V*

Denotes »- Denotes

Q-Turn no right turn alternative route

FIG. 5.2. Right-turn traffic diversions.

Besides enforcement difficulties the major disadvantage is usually to small traders who are likely to lose important custom. Tidal and Reversible Flow With heavy inward or outward peak flows there is an advantage in utilising additional lanes in one direction, particularly where the direc­ tional split is over 70%. The ratio of directional flows should match the lanes available; theoretically, three lanes permit the operation of tidal flow but, in practice, one lane may be frequently blocked for short periods, causing excessive delay and dangerous manoeuvres by other vehicles. Similar considerations apply to standard width four-lane highways, but in some circumstances the two outer lanes can be in­ creased in width to allow, in effect, a "squeeze lane" while the two central lanes are narrowed by a similar amount. For widths in excess of 16-5 m of pavement, lane marking configurations for reversible flow are straightforward. The operation of reversing flows needs very careful control, prefer­ ably with physical separation of the reversed flow lane. It is achieved by signs and signals and occasionally movable barriers and bollards. Overhead signs on gantries consist of illuminated red crosses (fluores­ cent or neon tubing) sited over each lane, or signs with legends painted

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111

on rotating slats. Newer secret signs, using a large panel containing a matrix of about 150 lamps, can be lit separately from a control centre computer, to show a variety of messages and speed indications. A special purpose programme sets up a consecutive sequence of instruc­ tions for various control modes and in-built checks prevent erroneous messages and sequences. Combinations offlashingamber and red lights are additionally illuminated to signal hazards and stop traffic respec­ tively. In the design of high cost facilities, such as urban motorways and for bridges and tunnels, considerable operating savings are possible by providing for directional flow demands, but it is often difficult to ensure adequate levels of safety. MANAGEMENT FOR THE PEDESTRIAN The improvements of pedestrian movements and safety are no less important than for other traffic. The reduction of delay and the avoid­ ance of lengthy detours, particularly for those routes serving public transport operations, are best determined by the examination of main user routes. The most appropriate crossing points of vehicular traffic routes can be selected, and then measures implemented to control, channelise and segregate conflict points. The type of facility required is based on the availability of gaps in the traffic stream and the resultant delays likely to arise for road crossing by pedestrians (see Fig. 5.3). The major provisions include crossing points, with or without central refuges, traffic signals with pedestrian phases, independent pedestrian signals and complete segregation by bridge or subway. At main pedest­ rian crossing points, the road surfaces need careful selection, and the drivers should be presented with good visibility and as few other con­ flicting demands as possible competing for their attention. Guard-rails can be used to define routes and also protect pedestrians. Education and instruction are an important aspect of all management programmes and no less than with the pedestrian. The Green Cross Code has been developed to teach people, and particularly children, to cross the road safely. It sets out a sequence of six logical steps to be taught and understood, but it is not suitable for children less than school age. Children are extremely limited in their ability to judge both

218

Traffic Planning and Engineering

speed and distance, and also sounds directionally up to about 10 years of age. Furthermore, they experience difficulty in distinguishing between left and right. The code defines safe crossing places and the process of judging whether or not traffic is far enough away to cross safely. However, the inculcation of a correct approach to road use can only be developed through experience gained in the company of adults and in specific road-side classes.

0

200

400

600

Traffic

800 volume,

1000

1200

1400

veh/h

FIG. 5.3. Proportion of pedestrians delayed, and average delay to pedestrians, in crossing the road.

The alignment of pedestrian routes must be made attractive to the users and avoid badly lit and recessed areas. Ramp gradients should not exceed 10% and by careful siting the total rise and fall along a route should be kept to a minimum.

TRANSPORT FOR THE ELDERLY The elderly form a significant and increasing proportion of the population (9-5 million in 1975) and the majority now suffer a degree of mobility deprivation precluding them from enjoying even some of the basic facilities open to the rest of society. The affects of transport

Traffic and Environmental Management

219

on the size and distribution of shops, hospitals, surgeries and the likeli­ hood of close proximity of friends or relatives has diminished with the changed patterns of residential densities and the mobility of younger generations, although this does not include children who have reduced opportunities of cycling because of increased traffic flow and the con­ sequent dangers. Many of the aged also form part of the deprived fraction of the population who are disabled. Journeys by public trans­ port not only give rise to frequently long walks at trip ends but boarding and alighting are particular hazards for the infirm. One-man services mean that there is little certainty of assistance, or even seats for these groups; thus old people are only likely to make on average a third as many trips as the mean all groups, with their most frequent trip to shopping. Budget restrictions as well as difficulty in carrying goods tends to also make this journey more frequent than necessary. Thus the traffic planner has to decide policy implementation for the whole community taking into account the needs and characteristics of all subgroups in the population. Problems have to be identified by surveys and through social agencies and "solutions" directed to proposals yielding benefit to the handicapped as well as the widest cross-section. The principal areas of study are the juxtaposition of residences and facilities, road crossings and safety problems, provision of shelters and seats along footpaths leading to bus stops, better vehicle design to improve access, in-vehicle safety during deceleration or acceleration from stops, and reduction of pollution in streets to lessen bronchial complaints. A study of bus steps has shown that three of 180 mm should be provided. The worst features from a survey of the elderly, of typical services, were seen to be that the vehicle moved before the passenger was seated, waiting for the bus, carrying shopping and fears about the automatic doors. GENERAL MANAGEMENT MEASURES The review of legislation, enforcement methods, the improvement in theflowof information, the presentation of easier decision-making tasks and the observation and monitoring of accident rates are all a basic part of traffic management studies and policy. Congestion often arises

220

Traffic Planning and Engineering

from stopped vehicles, and the introduction of box junctions to prohibit vehicles entering a junction unless their exit is assured, is indicated by yellow cross diagonal striping. Clearways similarly prevent traffic stopping on the carriageway. Some simulation studies and on-street measurements have shown the importance of traffic management measures on fuel consumption. The less the acceleration noise the better is a vehicle's efficiency, resulting in both fuel and pollution savings. Acceleration and deceleration areas, larger radii, draw-ins with adequate tapers, one-way flows, wide area traffic control, demand responsive signals with increased cycle lengths, linked signalised "Pelican" pedestrian crossings and off-street loading and parking are some measures which improve the steady state in traffic flow. PUBLIC TRANSPORT

TRAFFIC MANAGEMENT IN PUBLIC TRANSPORT An increasingly important task in traffic management is the improve­ ment of public transport services. A primary objective of current trans­ portation planning strategy is to encourage more public transport use, and this can be achieved by restraint of personal vehicles and better service levels of public transport. It is necessary not only to improve services but also to provide additional facilities for travellers transferred, or restrained, from other mode use if the viability of an area is to be safeguarded. Once the specific objectives of the transport plan have been derived, for the respective areas in terms of movement require­ ments, standard traffic study methods are applied to a number of case studies. These include the location of potential transport interchanges on bus and rail systems and the siting and size of appropriate car parks. Estimates of existing and future traffic are required to determine gener­ ated and diverted traffic. Because catchment areas are likely to be changed, and route patterns affected, particularly for the remaining car drivers, schemes must be carefully assessed for environmental con­ sequences before making changes to the road network. In most cities and towns, the principal public mode is the bus and most of the im­ provements will be directed to improving their priority over other

Traffic and Environmental Management

221

vehicles. Longer term measures may include feasibility studies to build entirely new bus routes and where these are only likely to be utilised at peak hours, commercial vehicles could be permitted to use them at other hours, and so improve their economic viability. NEW FORMS OF PUBLIC TRANSPORT It is increasingly unlikely that new transit modes will be developed either for long (automated light guided rail transit) or short (high-speed passenger conveyors) journeys except in special situations where there are existing rights of way, or in new developments like airports and other types of interchange. Thus development is likely to be concen­ trated cm improvements and experiments with bus services and the exploration of a range of options such as the publicly sponsored bus demonstration projects in urban areas and the more recently instigated experiments applied to rural areas. The management of transport services for rural areas is assuming greater importance as the needs of the disadvantaged, deprived of mobility, are more fully recognised with the trends towards the centralisation of facilities, and the loss of local enterprises. In a number of the remoter areas, particularly Scotland, post office vehicles are permitted to carry passengers on the payment of a fare (post-buses), and some licensed car drivers, permitted to collect fares, is another possibility. Less sparsely populated villages are more appropriately served by minibuses, operated by local transport undertakings, but a number of successful "community bus" develop­ ments have been arranged locally where volunteer drivers provide a service for the local community. Shared "taxis" are also being used with individually charged fares, as well as school buses carrying pas­ sengers from depots and flexi-route minibuses, driven by professionals, offering a pick-up on demand service. Suburban areas have seen the development of public transport services offering "dial-a-ride" with small coaches or minibuses linked by two-way radio. The driver responds to telephone demands either collecting passengers from their homes or points close by. Modified services of this type, cheaper to operate, cover a fixed route system but can react to a telephone demand, either following an unconstrained

222

Traffic Planning and Engineering

diversion, or one pre-restricted to a selected pattern of limited diversion. The degree of choice between alternatives helps ensure the availability of a service flexible enough to meet some of the principal local needs, although few of the disadvantaged have a telephone. However, while public transport provision is enhanced, generating new traffic, they attract few car drivers and mainly serve shoppers and recreational journey needs of women, children and the elderly. In other experimental services the social agencies operate hospital transport schemes for visitors and patient clinics, also emergency car services. Transport Interchanges The need to change from one service to another is a disadvantage weighted heavily by users. Even on rural to rural journeys one-third of passengers avoid those services requiring a change of service (two-thirds for rural to urban journeys) even though additional penalties are caused in fares or time. As journey length increases, resistance to service change increases as many travellers fear being isolated in places not well known. Thus there are special needs for well-designed multi-mode interchange complexes with convenient displays of all modal services, destinations, arrivals, car parks, platform positions, and general service needs of passengers for handling baggage and eating. Location of sites is important and should embrance all modes available in a town or city region. Bus Operating Studies The principal study measures evaluate user considerations in adopting levels of service and the separate interaction of the operator's revenuecost management. Bus-stop spacing is important, relative to the origins and destinations of passengers, determining the aggregate walking time to a pedestrian service. In the case of transfer traffic the location of common terminals is also critical. The distribution of arrivals and waiting times is necessary in the allocation of a service frequency, and is associated with the number of passengers alighting at specified stops. Thus it can be seen that the process is an iterative one, affected by the point a bus has reached on its route and its average loading and the

Traffic and Environmental Management

223

likely occupancy ranges. The method of collecting fares, one-man operated, season tickets, concessionary tickets, change machines, offbus ticket sales, type of bus and entry-exit doors, time of day and passenger characteristics (aged, shoppers, young families) affect the total boarding and alighting time. Line haul parts of the route affect the regularity of service, according to traffic conditions, and journey times are influenced by the provision, design and siting of bus bays. The integrity of a service must also take into account crew-manning considerations, lateness of arrival, breakdown and relief service pro­ vision occasioned by aberrations in the service. Overall stops are usually located at about 2-3 per kilometre. It has been said that supply creates its own demand, e.g. roads generate car traffic; whether or not this holds for public transport has not yet been demonstrated as a measure leading to a marked reduction in low occupancy car use for commuter journeys. The main aim of the bus demonstration projects set up by the Department of the Environ­ ment inferred that gains would be made by reducing private traffic and improving the environment, all without loss of commercial activity in city centres. In addition it was hoped that improved efficiency of public transport would result in financial viability of the services. By such improvements further restraint measures could be introduced and pedestrianisation schemes extended. However, cars left at home by drivers are usually used by other members of the family, worsening off-peak bus use. Thus studies need to evaluate a much greater range of flexibility in public transport services by supplementing trunk-routescheduled services with a range of intermediate forms of transport (often being operated in developing countries), more integrated "park and ride" and "kiss and ride" schemes in the larger urban coupled areas with concentrated destination demands, along travel corridors. The latter type of services require careful planning ensuring accessible parking (drop-off points for "kiss-and-ride" schemes), comfortable waiting, reliable and regular public transport, and limited controlled parking at destinations. Innovatory and Improved Public Transport Other priorities that have been tried, for instance with good results

224

Traffic Planning and Engineering

in Singapore, include the preferential treatment for high occupancy vehicles, daily licences, sometimes with time constraints, and charges varied to the vehicle's occupancy. The San Francisco Bay Bridge experiment allows a segregated lane for "pool" cars and a nominal charge, and the use of a special loop road in Minneapolis for both buses and "pool" cars. However, with all these and other transport innova­ tions problems arise of the nature of competition between public transport operators obligated to run services while paratransit owners make profits at their expense. Besides the innovatory forms of bus transit developments, scheduled services can also be effectively improved, e.g. by the introduction of higher quality services like the Stevenage "Superbus" (45 seats and 15 standee spaces) designed for a 47 km route and for one-man opera­ tion. Services offer a 5 min peak and off-peak with 10 min schedule in the evenings and at the weekends, flat fares (off-vehicle ticket purchase). The vehicles are designed with ease of access and are matched by route facilities such as covered shelters; all stops are request only with a maximum mean walk time of 5 min from dwellings, and the buses have a distinctive livery. General improvements in standard services can also be made by using fare boxes (2J s saving), no change given (£ s saving) season and period tickets {\\ s saving), all mode tickets and auto­ matically operated lower step and centre doors. More comfortable shelters are needed, and some countries now provide them heated and/ or cooled, with seats and information sheets.

MEASURES TO IMPROVE BUS ROUTES The principal methods include the adoption of bus-only lanes on suitable roads, either with-the-flow lanes or contra-flow lanes, bus-only streets and bus precincts. While these changes improve the flow and journey times between junctions, additional management measures are needed to reduce delays at traffic signals, regulate or prohibit parking or loading by operating bus clearways, banning turns for other traffic and granting exemptions to buses. It is often customary in Britain to physically segregate contra-flow lanes by a median, which also may be required or widened for with-the-flow lanes where loading and un­ loading is needed to service frontages alongside the bus lanes.

Traffic and Environmental Management

225

Traffic Studies for Bus-only Lanes For a comprehensive scheme a coarse study is made of all routes to identify operating conditions and congestion points. Detailed studies are then made of selected routes likely to yield suitable benefits. Observations are usually made by travelling observers equipped with stop-watches and tape recorders to record a sample of bus journey times and the distribution of delays due to stops, junctions and con­ gestion. Mean journey times, journey and running speeds are calculated from the data, together with the statistical attributes of the services. The number of runs required for a given level of accuracy is determined from the variability of the observations. Normally, about ten runs are sufficient, and these are spread over the days of the week, but avoiding special occasions such as school holidays and roadworks. Figure 5.4 illustrates the main features of bus lanes. It is essential that the routes are clearly defined by adequate signs and bold road markings to improve safety for all road users. Minimum lane widths are estab-

V

Stop line Bus lane terminates Lane —

Bus—'

V

Signals

Vehicle queue

With-flow bus lane

J"L

Divider and loading Ian

Confro -flow bus lone

^^.

if

»' FIG. 5.4. Bus lanes: with-flow and contra-flow arrangements.

226

Traffic Planning and Engineering

lished from vehicle characteristics but are currently not less than 3 m. Contra-flow lanes are often designed particularly to prevent lengthy detours of buses in one-way systems; in these cases, it is usually infeasible to permit taxi and cycle use, but is possible for them to share lanes in other cases. In congested lineal shopping streets, often found on important radial through routes, bus precincts may be a preferable alternative to pedestrian-only precincts. However, pedestrian safety must be carefully considered, and it is paramount where contra-flow lanes are operated. Bus-lane operations may be restricted to selected hours of the day, e.g. 8.00 to 10.00 a.m. and 4.00 to 6.00 p.m. While a primary objective of bus lanes is to enable buses to pass queues and slow-moving traffic, it is often necessary to maximise the saturation flow at traffic signals and prevent other traffic queues overlapping upstream junctions, it is therefore normal practice to terminate bus lanes 20-60 m upstream of the stop line and this also enables other traffic to make safer left turns. Where it is probable that peak flows may cause queues to extend over the preceding junction, it is necessary to install queue detectors to adjust the signal controller's cycle time and phase split. Signal Pre-emption In order to further improve the bus priority by ensuring that the bus clears the next signal ahead with minimum delay, it is possible to install special loop detectors in the carriageway which are activated by an. onboard bus signal generator. The detector relays a command to the signal controller which either terminates the cross-flow early, or extends the running green on the approach to enable the bus to clear the junc­ tion. To prevent queues building up on the side road additional running time can be subsequently allocated, when no bus is present on the main road, thus restoring some of the time lost to other traffic. Emergency vehicles can be similarly equipped to receive priority. Design of Bus-only Lanes From the data analysis the principal causes and frequencies of delay

Traffic and Environmental Management

227

will be located, and consideration can next be given to potential im­ provements which yield net community benefits. These may be the introduction of forms of signal priority, banned and permissible turns for all vehicles and bus laybys, besides the introduction of bus lanes. Bus laybys may also be required on bus-only lanes to prevent un­ necessary stops where there is a high frequency service. The effects of bus schemes on pedestrians must be carefully assessed, and zebra crossings may need replacing by the pelican type. Frontages may also be adversely affected by the operations and diversions of traffic onto unsuitable roads. This causes environmental deterioration and increased hazards and effects on parking, if this has been previously permitted. Particular attention must also be given to enforcement and regulation problems. Assessments of Public Transport It is usually essential to undertake a comprehensive cost-benefit analysis, taking into account bus passengers, and the costs and benefits to transport operators. By considering only operator benefits, in the case of one-man bus operation, heavy disbenefits have been incurred by other groups of users due to the increased delays imposed by longer stopping times. Cost-benefit analysis is used to compare the relative net benefits of alternative schemes and the before-and-after effects on vehicle operating costs, crew costs and passenger costs. The coordina­ tion between transport operator, police and traffic engineer is essential to achieve maximum community benefit from management measures. Where services are subsidised it is essential that the maximum benefit is gained by users identified within the transportation policy framework, and that resources are directed efficiently towards achieving the ob­ jectives. The LGORU model, TRANSEPT, has been used to find efficient bus networks after data collection and calibration has been conducted for a specific town. Reviews are made of the physical prob­ lems associated with recommended routes, removal of services and journey times to show the impact on levels of service by restructuring of the services (generalised costs), operating revenues and costs, and any special effects caused by the use of new routes (operational factors). The effects of economies on existing services are important if resources

228

Traffic Planning and Engineering

are to be available for the development of alternative or new services of the type outlined earlier. There are often a number of choices in econo­ mic management which entail ranking, by some suitable method, of the available options. Generally the maximum operator savings, on scheduled services, causing the lowest user disbenefits are achieved by reducing peak hour services by 5-10% and, thereafter, peak hour route coverage. Most other types of measure yield far lower operator's savings relative to the disbenefits to passengers, but in some situations curtailment of early and late services, the withdrawal or reduction of weekend operations should be investigated. Fare increases, as a measure of yielding relative savings, are not as effective. School transport provision is a costly rural service for local authori­ ties obligated to provide free transport to all pupils residing at greater than a set distance from their schools. Manual scheduling is time con­ suming and difficult to evaluate vehicle size, pick-up constraints and doubling routeing in relation to distance and time costs. The ROUTE MASTER package, based on a look-ahead technique, assesses the implication of accepting each new link for inclusion in the subsequent total route pattern and schedule. The use of staggered school hours has been shown to give worthwhile benefits. General policy advice on bus priority is also laid down by the Department of Transport in recom­ mendations to local authorities. CONGESTION AND RESTRAINT The alleviation of congestion is a growing problem because of its effects on trade, public transport viability, and the inevitable environ­ mental consequences to society. Traffic management measures, if soundly based, permit greater traffic flows to be accommodated more safely on the existing road system with some benefits in time savings to travellers. While some management schemes have been detrimental to the environment from their inception, the overall deterioration has been due to the steady growth in personal travel generated by car ownership. This traffic growth has steadily eroded the benefits obtained from the original management measures; often the opportunities and necessity of building a primary urban motorway network have been lost and with

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229

it the creation of environmental areas. Consequently there has been a steady and spreading deterioration of unsuitable conditions to all parts of the city. Current objectives in management are to seek for ways in which to impose restraint in traffic growth and use. The principal methods of traffic restraint are legislative, parking controls, physical restraint, supplementary licensing, cordon pricing, road pricing and fuel taxes. Legislative, parking controls and physical restraints form a distinctive group in that they can be considered as non-fiscal measures. Legislation has been used to control and regulate the nature of traffic since Roman times, but its use must be broadly acceptable to the community for political reasons. Parking has been and remains a principal method with the allocation of space, by area, capable of implementation at any level determined by the authorities, provided that all on-street and off-street sites are controlled; practical restraint is a combination of the supply of spaces and their price related to the duration of demands. Physical restraint places limits on road space by reducing capacity, usually by signal systems that enable priority to be given to selected vehicle types. Other methods include narrowing roads ("throttle points"), turn prohibitions, pedestrian streets, cycle roads and bus streets. The other measures are entirely fiscal with supplementary licensing required by vehicles using or present in a controlled area; a licence is purchased from an outside source (licensing centres, shops and mach­ ines) and is displayed for the paid duration. Special categories can be allowed for within this system of control, e.g. residents, doctors and shopkeepers. Cordon pricing only differs to the extent that a charge is paid at a toll point, but vehicles within the area are excluded from the control. Road pricing can be effected in a number of ways, varying from simple time expendable meters to complex variable rate systems, where the charges are automatically metered. The favoured system is one where vehicles have a distinctive identity transmitted to roadway detector loops, located at intervals in the road network; the number of crossings of loops is registered and their owners are sent periodic accounts for their use of the road system. Charges can be varied to suit traffic conditions or forfixedtime periods of the day. Such sophisticated systems are only suitable for towns in excess of a quarter of a million population and numerous practical difficulties remain unresolved.

230

Traffic Planning and Engineering

Generally, parking controls remain the most suitable system imposing the least additional overall costs on vehicle users; it is also well tried and understood, but it is estimated that parking charges have to be relatively higher to achieve the same results because they only restrain journeys ending at a particular destination and do not directly dis­ courage the use of roads generally. Road pricing affects the proportion of through journeys in an area. Similar discriminatory problems arise with differential fuel tax policies. Traffic planning strategy should encourage a more positive approach, creating suitable alternatives by long-term changes in urban layouts, encouraging some types of journey and discouraging others, while investing in alternative forms of transport. Restrictive policies in isola­ tion tend to induce enforcement and administrative problems. Since the introduction in London of controlled parking schemes (in 1960) the issues of thefixedpenalties has risen almost tenfold from under 100,000 to nearly a million and the number of wardens has increased from less than 200 to over 1500. At the same time courts and police have become overburdened and a large number of offenders escape the consequences of their misdemeanours. FREIGHT INTERCHANGES There are many areas of derelict land, adjacent to nodal points in the transport system, where interchange between freight services could be improved, often in the heart of the industrial metropolitan areas. The proximity of rail sidings, access to the national motorway network and preferably also to coastal or inland ports is a prerequisite for an inter­ change location. Information services, with access to computer termi­ nals for return load traffic, loadings, arrival times and stock control, warehousing and distribution depots, maintenance and loading facili­ ties, and the range of services facilities for personnel are the main requirements if the costs and effectiveness of freight movement is to be realised, and in the setting of wasted resources and energy consumed by the currently large proportion of empty load space. Some interchanges would also need to be sited near to or on the periphery of major freight airport terminals. In the same way that containers are now the principal

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231

medium of international freight traffic, and have led to many technical innovations as a result of standardising operations, similar advantages can be gained in standardisation of break bulk loads for convenient transfer operations to smaller vehicles in a manner similar to the barge systems developed for sea traffic. Such developments would seem ideal for improving the scope and range of lorry parks. SEGREGATION MEASURES Traffic Segregation While the principles have been widely applied to segregating vehicles and pedestrians its potential utilisation for other purposes has not been adequately realised. Segregation not only permits the designer a more specific brief in meeting the basic requirements of particular categories of user more precisely, and with less compromise, but ensures a more amenable and comfortable environment for their needs and encourages a better performance of a less taxing nature. A purpose-built facility is often more cost effective and can be located, and integrated with sur­ rounding land-uses, with the least intrusion and disturbance. Pedestrian Segregation Complete segregation of pedestrian and vehicle is often difficult to achieve in existing urban layouts but all new developments should permit a design, for each type of use, taking special account of indi­ vidual characteristics and requirements. In central areas, for acceptable pedestrian operation, shops, offices, public buildings and entertainment places must have direct and rapid access to public transport and carparking facilities. Differences in vertical level for the main walkways should be kept to a minimum. Where height differences are unavoidable they should be catered for by ramps, escalators and moving walkways rather than steps. Generally many of these requirements demand the regrouping of individual units into single blocks offering full access facilities. Provision for loading and unloading by rear access or under­ ground connections to premises will, together with the removal of

232

Traffic Planning and Engineering

parked street vehicles, considerably reduce the accident potential within commercial developments. New residential areas must depend to a large extent on the design of suitable road systems fulfilling their special function. Centres of gravity of individual parts of the large estate must be close to a major feeder route carrying public service vehicles into the town's main road system and connected at stopping points by special bus draw-ins constructed with pleasantly designed enclosed shelters and seats, timetable displays and directly connected to the main covered walkways. Where neigh­ bourhood centres are provided with shops and recreational buildings there should be separately located and segregated footpaths to the various parts of the estate. Other roads should specifically only provide access to and from an individual's residence or garage, and not permit through access. An example of a segregated residential area is shown in Fig. 5.5. The design problems for traffic in new areas (see Fig. 5.6) are far more easily dealt with than those in the existing towns built without the num­ bers of present-day road vehicles and levels of activity in mind. In old towns segregation of pedestrian and vehicle can only be accomplished on a more limited scale. However, many examples of pedestrian streets have been introduced into a variety of towns and cities reducing accident rates and improving amenity and, often, trade. This is achieved by diverting through traffic away from pedestrian areas, constructing peripheral parking facilities and providing new public transport routes and interchanges. Servicing premises is sometimes difficult and best overcome by constructing rear service access or underground roads, but if these alternatives are not possible regulation is resorted to by restrict­ ing servicing to times outside the principal shopping hours. In such circumstances very careful design, warning and control has to be intro­ duced to prevent accidents to pedestrians conditioned to a vehicle-free environment. An alternative method that is practical, provided that distances are not too great, is the breaking down of loads into small lots and trolleying the consignments to individual shops and offices, where these are not too large. In areas where vehicular traffic is unavoidable, and particularly at junctions, it is possible to install a limited measure of segregation for reasons of safety by erecting guard railing. This prevents crossing at

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233

FIG. 5.5. Segregation in a residential area.

other than selected points, and pedestrian controlled lights can be in­ stalled to further separate vehicular and pedestrian movement. At sites with very heavy crossings of pedestrians it will often be desirable, both because of delays to traffic and the safety of pedestrians, to construct subways, with suitably located ramps to encourage their convenient use. A major site difficulty is inevitably the high cost of modification to services, but this can be minimised and at the same time pedestrian ramp gradients reduced if the road is raised relative to the adjacent footpath. The major objection to this method is generally not the cost but difficulties in narrow streets of obstructing frontages and the dis­ charge of exhaust fumes at a particularly annoying height, but this can be overcome by constructing walls. Separation of turning and direc­ tional vehicular movements enables the engineer to locate refuge areas

234

Traffic Planning and Engineering

across the main lines of flow and so assist road users by simplifying their decisions and improving safety. In a similar manner, one-way streets can reduce accident potential by a reduction in the number of types of conflicts present at a junction. Physical severance of a unit activity into disparate parts usually leads to loss of efficiency, but the psychological severance of an individual's activity are even more difficult to assess. In some cases even physical separation is a prized asset retaining particular cultural or community identities. Severance effects due to new routes are generally reduced by constructing subways or overbridges, but ideally the pedestrian routes should be designed to remain at existing levels, and aligned on desire "line" movements. Cyclist Segregation Segregation of the cyclist is no less important than of the pedestrian. Whatever proportion of a car passenger unit is considered appropriate the fact is that the road width occupied by cyclists, often in pairs, is effectively nearly a lane, and, due to their relatively low speed and

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235

instability, they are a potential danger to themselves and to drivers. Cyclists on their own tracks need less space because of the lower relative speed differences present than on the road and, like the pedestrians, require less than a quarter of the construction depth of road pavements. This represents a considerable saving in construction costs. In view of high accident rates, more than ten times that of cars, careful considera­ tion should be given to the provision of multi-purpose cycle tracks accommodating pedal cycles, mopeds and scooters but with some form of effective speed control. Mixed Traffic Areas In some cases complete segregation is neither possible nor necessarily desirable, and this leads to different types of traffic sharing a common area. Generally preferential treatment will be accorded to the "weaker" elements of the traffic mix, e.g. pedestrians. There is also a developing policy of converting traditional streets into multi-functional areas. The previous rigorous adoption of standard street and footpath widths has largely been responsible for deteriorating visual standards and the quality of pedestrian and cycling movement. These multi-function areas have been shown to be as safe, where properly designed, as traditional layouts but permit enhanced freedom of movement to pedestrians, while simultaneously allowing limited and controlled vehicular access. It is essential that the pavement extends from wall to wall, with kerbs and separate areas completely removed, and that long straight sections are eliminated by narrowing and curving the spatial manoeuvre areas for vehicles, by tree and shrub planting, varying surface treatments, adding bollards and lighting with alignment changes made abruptly. Speed is further controlled by rutting and surface bumps ("sleeping policemen"). Areas are provided with plants in containers, seats are added and pro­ vision made for bicycle stands. Vehicle Segregation Reduction in exposure risk by the segregation of pedestrian, cyclists and motorists can further be achieved by the segregation of vehicular

236

Traffic Planning and Engineering

traffic. External and internal traffic to towns can be separated by the construction of bypasses and ring roads within towns; through and stopping traffic can be separated by the provision of through and local routes, creating environmental areas. Small towns and villages, astride important routes, are often made intolerable by through traffic. Motor­ ways can often replace a number of such routes through a region, allowing the existing network to revert to local use, and improving safety and environment simultaneously. With an increasing proportion of cars within the total traffic flow the case for car-only roads is emphasised. Considerable construction cost savings can be made because lane widths can be narrower, headrooms beneath structures can be lowered by about a third, and by using steeper gradients the total interchange requirements in land, roadworks and structures are minimised. Structural and pavement costs are reduced and the visual impact on the environment is less. Better opportunities are created for inserting new roads into urban areas as curvature and greater route diversion are not so dependent on benefits from the time savings of commercial vehicles. Similar benefits can be granted to public transport by the purpose building of new bus routes, possibly shared with commercial vehicles. Both categories of vehicle generally need to penetrate to the core of activities whereas this is not a basic requirement for the majority of private cars. Fortunately, from a traffic viewpoint, the peak uses of the two categories do not coincide, and thus road space is capable of maximum use over an extended time period. The likely joint benefits would justify such purpose-built roads which presently are not economically viable when considered individually. Other important segregations of traffic are made by direction (central dividing strips), by turning movement (storage lanes), by speed con­ ditions (speed change lanes), traffic signals (separation in time) and by other traffic control measures such as one-way streets.

ENVIRONMENTAL STUDIES AND ASSESSMENTS

The demand for greater travel results in increasing trafficflows,which may arise on existing roads or be accommodated on new routes, par­ ticularly urban motorways. Both situations can lead to environmental

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237

problems caused by traffic noise, visual intrusion, air pollution and vibration. The insertion of new motorways into urban environments can also generate secondary traffic effects which radiate outwards from interchanges, along feeder routes, and cause a marked deterioration in environmental conditions to people not previously affected. Traffic management schemes may also have marked environmental consequen­ ces. It is thus more than ever necessary for the engineer to estimate, by careful study, the impact of traffic measures on the overall quality of life, and to ensure that steps are taken to ameliorate the disturbances to individuals. Finally, that the aggregate result is of total benefit to society. Environmental Management Because of congested main roads commuter traffic often uses alter­ native routes following main roads through residential areas, severely affecting environmental and safety standards. Standards of amenity can be protected by road closures but disbenefits may arise to commercial activities within the affected area and induced changes are likely to increase traffic on peripheral roads. However, these additional incre­ ments of traffic have a lesser compound effect in disturbance to residents than the gains elsewhere; thus there are likely to be net improvements in environmental conditions overall. The development of environmental areas calls for detailed study and the careful evaluation of alternatives; route changes in small areas can result in marked differences in traffic flows. While such proposals for environmental improvement are usually the subject of consensus, there are marked dichotomies from different group interests of the population. Consultation leaflets and explanatory meetings are followed by attitudinal surveys to gauge the likely com­ munity response to a range of proposals and to highlight deficiencies in schemes. In the use of attitudinal survey techniques, thorough and specialised preparatory work is necessary, and misleading interpreta­ tions arise with inappropriate scaling techniques. The creation of environmental areas in management plans tends to benefit residents on internal roads at the expense of those in the heavily

238

Traffic Planning and Engineering

used peripheral roads. Locations adjacent to the outer part of a zone are most preferred where public transport is routed onto the boundary roads because then internal and external accessibility is maximised for minimum environmental disturbance. Few car users are prepared to trade the status quo for improvements to public transport services, although they welcome improved public transport services without other changes being imposed. Small shopkeepers are disturbed about the possible loss of passing trade through rerouteing, and factory owners fear increased delivery problems or difficulties in locating their premises. Thus surveys of visitors to an area and their special needs require close study before implementing changes. There are now many standard computer program suites available for analysis of data with social characteristics, such as the statistical package for the Social Sciences (SPSS). For the assessment of each type of disturbance, there are four principal categories of investigation, dealing with generation, propagation, possible effects and methods of reduction or control. Noise Noise is best described as unwanted sound and its measurement therefore imposes considerable difficulties, as it will vary between individuals and with situations. Sound is energy propagated from a source in a longitudinal wave travelling at a velocity of about 340 m/s through air at sea level; because the disturbance regularly repeats itself they are harmonic waves and characterised by a definite frequency and wavelength. The average power transmitted by a sound wave, per unit area, is called the intensity / but is conveniently measured as a sound pressure (P in /xN/m2 as IccP2). The simplest form is a pure tone with a frequency/= 1/rfrom its sinusoidal form, T being the maximum amplitude of the signal within the time period T. Most sounds, however, vary with time in frequency and magnitude, and are thus not pure sinusoids. For a pure tone of single frequency, e.g. from a tuning fork, one whole change in the cycle is called the period of the wave and is measured in Hertz (1/frequency in c/s). The product of the wavelength and frequency equals the wave velocity. Sound waves cause an oscillation of the ear drum, whose sensitivity

Traffic and Environmental Management

239

varies with age, sex and frequency. The minimum sound perceived is 20 /xN/m2 (threshold of hearing) and the maximum, at the pain thresh­ old, is about 100 N/m2. The difference between the two pressures is in the ratio of 1:5 x 106 and, for practical reasons, sound pressures are usually expressed in a relative scale of decibels. The decibel is thus defined as ten times the logarithm to the base ten of the ratio between two quantities of power. Because the sound power is proportional to the square of the sound pressure a suitable noise scale is defined as follows: sound pressure level = 10 log10 [~-Λ = 2 0 log10( -i dB, where Px is the sound pressure being measured and P0 is the reference pressure based on the threshold of hearing. The range is now from 0 dB to 120 dB. Because the scale is a multiplicative it is necessary to add together the intensities (powers) and not pressures in order to sum the loudness of sounds, e.g. two almost equal sounds increases the level by about 3 dB while ten almost equal sounds increases it by 10 dB. Each time the sources are increased tenfold, add 10 dB to the sound level. Also a doubling of the distance from a source produces a change of 6 dB (the surface area of space surrounding a source is a sphere, hence doubling the radius increases the surface area fourfold). The loudness of a tone is given in phons (P = 2(P_40)113); an equivalent loudness of n phons equals that of the standard tone at n decibels above its zero. A subjective scale of sones (S) is formed so that the apparent loudness ratio of two sounds assessed by observers is given by the ratio of their sone values and S = 2 (P-40) / 10 . Most traffic noise measurements are weighted with respect to the response characteristics of the human ear. Sound Level Measurements A suitable microphone and amplifier will respond to sound pressure levels and indicate frequency levels. By attaching a filter, which reduces or screens frequencies outside those to which the ear responds, a scale of equivalent values, for human hearing, are obtained by the so-called

240

Traffic Planning and Engineering

A, B or C weighting levels. For traffic noise measurements the A weighting is used and measurements are made in dB(A), with diminish­ ing weight given to high- and low-frequency sounds. There are a variety of instruments available ranging from simple peak recorders to meters with statistical distribution analysers that use filters to determine the proportions that differing frequencies contribute to the overall sound. Each type can be set up at sites alongside the road and observations taken at predetermined time intervals, or recorded on a chart by means of a pen, either in the field or the laboratory as shown in Fig. 5.7. Statistical analysis enables the field records to be fed, at set time intervals, to a counter for up to twelve ranges of sound levels. From the counter record, a cumulative frequency curve can be drawn, enabling percentile values to be deduced, as shown in Fig. 5.8. The percentile values L10, L50 and L90 refer to the sound levels which are exceeded 10%, 50% and 90% of a specified time. 100,

1,000

2,000

3,000

4,000

Traffic flow, veh/h FIG. 5.7. Noise levels near motorways.

5,000

Traffic and Environmental Management

241

u» 6 0 0 0 c i? 5 0 0 0 c 3 O

o E -4000 o

\-

§ 3 000 o

> « 2 000 .Q O



o

"5

1000

ε 3

o 50

55

60

65

70

75

80

85

90

Sound levels, dBA FIG. 5.8. Sound levels, cumulative frequency curve.

In practice the L10 levels are important and have been used to specify disturbance (indoor levels) by the Wilson Committee. These are also used in the computation of the Traffic Noise Index (TNI), developed by the Building Research Station, to indicate noise annoyance by a com­ posite weighted variation, obtained from data for straight, level and free-flowing roads in London at fourteen sites with interviews of 1200 residents. The earlier London noise survey measured levels at 540 sites and assessed the reactions of 1300 residents. The TNI is as follows: TNI = 4(L 10 -L 90 )+L 90 -30. It is usually obtained by measuring levels for 100 s in each hour for 24 h. Subjects generally suffer greater annoyance from high peaks occurring in low background levels, e.g. a motor-cycle accelerating at night in a quiet residential area. Table 5.2 indicates the effects of noise with examples. Other studies have also quantitatively related physical measurements of traffic noise to resulting dissatisfaction. The average of L10, from 0600

242

Traffic Planning and Engineering TABLE 5.2. Effects of Noise and Examples of Noise Levels Noise effects

<υ Λ

Blast deafness Pain Threshold of feeling

03

Q

Decibelsi 150 140 120 110

Typical examples Explosions Engine tests Thunder, gunfire Pneumatic drill Aeroplane

i r\(\ 1UU—

Reduced working efficiency c o c < c

Occupational deafness Interference with normal speech Annoyance

90 85 80 70 65

Underground railway Busy street Noisy factory Noisy office Suburban train Factory

(LC\

ou—

V)

> •Ό C 3 O

o3

Typing office Restaurant or general office

50

Private office Lecture room and suburban living room

45 40

Suburban bedroom and library

30


3 a 8 <

Country road Quiet conversation Whisper

^π zu— Very faint

Large shop Quiet office Average house

10

Quiet church Sound-proof room Threshold of hearing

to midnight, outdoors on a weekday is a useful approximation of dis­ satisfaction. A Swedish study has indicated the following relationship, based on the level equivalent (L eq ) to the energy mean of the fluctuating sound levels: L e q = 10 1 o g - ^ S 1 0 ^ / l %

Traffic and Environmental Management

243

where Z^ is the median sound level of the 5 dB(A) interval / and fi is the percentage time that a sound level is in the zth interval. Robinson has developed the Noise Pollution Level (LNP), applicable to general noise disturbance, including aircraft and road traffic: LNP = L eq + 2-56s, where s is the standard deviation of the instantaneous sound level con­ sidered in time over the specified period. Vehicle noise increases with its size, power and speed and is influenced by such operating conditions as gradient, surface texture and manoeuvr­ ing. While exhaust noise predominates up to 40 km/h as speed in­ creases, aerodynamic and tyre noise form a greater proportion of the total emissions. The volume, composition and consistency of the flow are predominant factors in the general noise climate, as shown in Table 5.3. The effects of noisy vehicles in interrupted flow conditions are much greater than in free flow states. TABLE 5.3. Mean Values of L10 in dB(A) at Building Fagade for Tabulated Distances from Source Speed (km/h) at flow 5000 veh/day

50 70 100

Without barrier Distance from source (m)

With 2 m high barrier Distance from source (m)

Traffic flow correction. Add to all values in table

10

25

50

10

25

50

Veh/day

Add dB(A)

70 75 80

65 70 75

60 65 70

58 63 68

52 57 62

46 51 56

10,000 20,000 50,000

2 4 7-5

Energy is dissipated in doing work and thus sound pressures are reduced by atmospheric absorption, ground wave, wind, buildings and land form. As an approximation, each doubling of the distance causes a drop of about 6 dB(A) in L10 and L50 levels, but for background levels, Lw, the approximation is about 3 dB(A) for each doubling of the distance. A further rough guide of the subjective impression of noise indicates that each reduction of 10 dB(A) corresponds to a halving of the apparent loudness.

244

Traffic Planning and Engineering

Noise control can be achieved in three principal ways. The first is by reducing the noise at the source by better vehicle design and more stringent legislation to ensure that vehicles are operated and maintained within the relevant levels, as shown in Table 5.4. Secondly, because traffic characteristics also affect noise levels, design and management of traffic can be effective in reducing noise levels at critical sites. Finally, by planning areas with sufficient shielding and designing buildings with adequate sound insulation, noise intrusion can be controlled (see Table 5.5); walls of 115 mm (4£ in) and 230 mm (9 in), without windows, reduce noise by 45 and 50 dB(A) respectively. There are many ways of achieving this, varying from siting the road in cuttings, earth mounding and contouring, constructing carriageway edge barriers, siting less noise-sensitive buildings such as warehouses, garages and factories alongside the line of route, or by cladding buildings with a noise shield. Figures 5.9 and 5.10 illustrate the relationships between noise, motor­ way construction and the siting of buildings. Noise Regulations The Noise Insulation Regulations 1975 were first made in 1973 under the Land Compensation Act 1973 (sec. 20) to provide rights to insula­ tion, for residential properties against traffic noise from new and TABLE 5.4. Maximum Permitted Noise Levels for Motor Vehicles (see BS 3425: 1966)

Vehicle type Motor-cycles > 125 cc capacity Passenger vehicles (< 12 passengers) Goods vehicles not exceeding 3£ tons Goods vehicles > 3i tons and buses

Construction limit dB(A)

Use limit* dB(A)

86

90

84

84

87

82

85

92

84

89

92

89-91t

EEC recommendation

* Use limit 3 dB(A) above construction limit for vehicles registered after November 1970. f Depends on bhp.

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245

TABLE 5.5. Average Noise Reduction Values Reduction in noise level

Window

dB(A) 5-10 15-20 20-25 25-30 30 40

Open (single Closed (single) Fixed (single) Fixed plate glass (6 mm) sealed Sliding (double) (twin 4 mm) Fixed (double) 200 mm gap

r < ;■* ^

>.

V

\

Traffic barrier

™/ ro / - I s /

,

25

\

.

t /'

0

V.

\

N N

\ \

0

I 25

3m Barrier wall Open aspect ( I ) Surface motorway v

\ \

75

50

too m

Structural barrier

\

\

\

< \\CD jro

IN

m "O



3 m Parapet wall Open aspect ( 2 ) Elevated motorway

<

^irk ^ 100

75

CD

^ 50

5° Preserves visual link \ ro

V \ X

ί 25

25

3m Retaining wall (3)

50

Grassed embankment

Sunken motorway

FIG. 5.9. Noise levels from motorways.

75

i

loom

246

Traffic Planning and Engineering

A

Aspect Distance "separation^

Jg g

Stepped blocks \J Γ

0 Π n

yJL

Housing Car parking

Industry or Warehouses

'&

ü

A Housing

ft^n „n r r r m ^ Η ^ π 4

H - ^ .

FIG. 5.10. Building near motorways.

improved roads, and include a 15 year provision. They specify the eligibility of property, within 300 m of the highway, for compensation by way of noise insulation work to be carried out when occasioned by noise conditions. The specified conditions include an L10 of 68 dB(A) (67-5 dB(A) in practice) normally obtained as a mean of all hourly L10s between 0600 and 2400 h on a working day, i.e. L10 (18 h), but here estimated for a 15 year period from the date of a road being opened to traffic (or the completion of alteration works) and being greater than the pre-works level by 1-0 dB(A) within the same time period, together with an effective contribution of at least 1-0 dB(A) from the traffic on the highway being considered. This means that if the new noise were to be terminated the resultant level would be at least 1-0 dB(A) lower. The noise from an eligible road must not be more than 6 dB(A) below the combined noise of all other sources, thus the minimum threshold is 60-5 dB(A). Calculation of Road Traffic Noise, HMSO, 1975, gives a guide, with numerous worked examples, to the methods of prediction. If site measurements are used the reference positions are taken at 5-15 m from the carriageway edges with the source level 3-5 m from the nearside and in a line 0-5 m above the surface. If the central divider between dual carriageways is more than 5 m, or where outer edges have a height difference in excess of 1 m, they are treated separately. Allowance is made for ground attenuation related not only to distances and heights but soft and hard ground surfaces. The effects of speed/flow

Traffic and Environmental Management

247

relationships, percentage of heavy goods vehicles, gradients, road surface grooving are also taken into account for all contributing sections adjacent to an observer's position, but direct vision of the "new" work is no longer an eligibility requirement. A polynomial relationship is used to calculate the levels with barriers, and an overall computational accuracy is specified. The sum allowed for remedial work is the actual or reasonable cost incurred, but the resident, affected by traffic management measures or generated traffic, has no entitlement to compensation even though the effects may well be worse. In particularly quiet existing areas relatively very large increases in sound level may occur and yet not reach the specified thresholds. A National Environmental Census in 1972 indicated that L10 (18 h) sound levels exceeding 75 dB(A) were mainly generated in the London area (nearly 80%) with 6 % affecting residents at densities of 25-100 p/h. Exceedingly small numbers of residences at densities less than 2 p/h suffer any levels above 60 dB(A). Vibrations Traffic vibrations are usually too low to cause structural damage to buildings but may create unpleasant and worrying sensations, as can be experienced when standing on a footbridge crossing a major traffic route. Generally, because many surfaces are relatively smooth, the vibrations from motorways are less than those on corresponding urban main roads. Vibrations are described by the amplitude, velocity and acceleration of the particles or surface affected and the number of completed cycles in a time period, i.e. the frequency. Peak values are usually measured and, in the case of a phenomenon with a sinusoidal relationship, are related as follows, although approximately for most vibrations: 2π x frequency =

acceleration velocity

velocity amplitude

Measurements are generally made with instruments recording ampli­ tude, velocity and/or acceleration by using a transducer to convert the energy into a direct reading electrical or mechanical signal.

248

Traffic Planning and Engineering

Traffic vibrations are caused by variations in the load transmitted to the road by the vehicle's suspension and by impact with surface irregu­ larities. The frequency / of vehicle-induced vibration is represented by the formula

2^/y where M m ^ g

= = = =

m

d

total vehicle weight, unsprung weight, static deflection of tyre, acceleration due to gravity.

Most frequencies from vehicles are in the range 7-20 c/s and reson­ ance is likely to occur with silty soils resulting in larger amplitudes, but these, in any case, are small. Most vibration is transmitted through the road pavement directly to the supporting soil mass. Because of the complexity of the systems involved there is a considerable variability in results, due to the differences in materials and the relationship with distance, but it is generally accepted that for short distances amplitude and velocity varies inversely with distance as shown in Fig. 5.11. Air Pollution The effect of air pollution is felt by a deterioration in the health and performance of man, animals and plants and can create an intolerable or poorer environment. An insiduous accumulation of lead within man is of particular concern because the long-term consequences are not fully known or appreciated. The rapid increase in lead levels is largely as a result of the motor vehicle industry. Air pollution is generated by homes, industry and motor vehicles and, while the Clean Air Acts have marked effect on background levels, that of traffic is increasing and becomes more noticeable. The concentration of emissions is reduced in proportion to increased distance from the source, although in un­ favourable meteorological and topographical conditions photochemical smog may be formed as in Los Angeles. At a lesser level unpleasant odours are generated, and while the sense of smell fatigues relatively

Traffic and Environmental Management

249

12-75 r-

5 0 0 l·—

2-501

3

0-5—

ε < 0-l25l·—

0-05 h -

0 0 2 5

2-25

4-50

9-0

180

360

Distance from centre line of vehicle to observer,

72-0

m

FIG. 5.11. Vibration amplitude by distance and type of vehicle.

rapidly, heavy traffic maintains smelly emissions and particulates in the air at levels far in excess of threshold values. The presence of the ben­ zene group can be detected at levels as low as 4-7 ppm with the phenols even lower at 0Ό5 ppm. While the major contribution to air pollution from the car is exhaust gas, others arise from the fuel tank, carburettor and crank case. If oxidisation of the fuel was complete in an internal combustion engine only water and carbon dioxide would be emitted; however, carbon monoxide is found in large quantities together with other compounds and unchanged fuel. Lead additives are also used for "anti-knock" reasons adding the dangerous lead components to oxides of nitrogen.

250

Traffic Planning and Engineering

Diesel and petrol engined vehicles have similar exhausts although the former has a lower proportion of pollutants, but increased smoke and smell if not correctly maintained. Some of the effects, particularly of continuous or prolonged exposure to low dose rates, are not known for the pollutants. Unburnt petrol has slight anaesthetic effects in high concentration; aldehydes cause irrita­ tion of respiratory system and eyes; aromatics (benzpyrenes) are known carcinogens but are present in relatively low levels; carbon monoxide is preferentially absorbed to that of oxygen by haemoglobin, depending on concentrations, exposure and activity of recipient. Small amounts of carbon-haemoglobin impair mental ability temporarily, but the levels are generatty much lower than that occurring in smoking. The oxides of nitrogen have been shown to affect other primates causing lung damage, while lead is not only injurious but is taken-up in biological chains, thus creating a double danger. Effective control can only be exercised by reducing engine emission through such modifications as catalytic converters fitted to the exhaust system, afterburners, re-design of carburettor and combustion cham­ bers, air injection into the exhaust manifold and other basic engine changes, crank case re-feed of gases to combustion, or new fuels. Lead additives need to be reduced in any event because they also impede the working of pollutant control devices. Besides setting basic standards for pollution control, problems of enforcement arise because of the complexity testing, which is normally carried out only on the production line, and poor maintenance of vehicles requires suitable apparatus for spot tests. Traffic pollution has been measured at a number of sites in Great Britain as shown in Tables 5.6 and 5.7. Severance Severance results from the division of an area by roads and traffic. The worst effects of separation can be minimised by careful design and often additional costs. These may be incurred during construction, i.e. elevating a route to prevent interference with the local movement pattern or depressing it to facilitate overbridging; or during operation by increasing vehicle distances, i.e. locating routes on the boundaries of

Traffic and Environmental Management

251

TABLE 5.6. Air Pollution Pollutant Sulphur dioxide Og/m3) Smoke Og/m3) Lead (/xg/m3) Carbon monoxide (ppm) Nitric oxide (pp 100 m) Nitrogen dioxide (pp 100 m) Hydrocarbons Og/1000 m3): Fluoranthene 1:2 Benzpyrene Pyrene Coronene Anthranthrene 1:12 Benzperylene 3:4 Benzpyrene

Blackwall tunnel

Fleet street

—

384 430 3-2 23

202 27-2 120 121 10 110 18 98 22 7 51 31

— —

—

26

—

20 6 46

—

London av. London background smog levels 1957

—

—

35 2 11 3-3 2-4

670 5 360

2-5 20 2-5 10 0-5 2-5 50

407 74 317 28 38 106 222

TABLE 5.7. Pollutants Pollutant

Regression equation

Average carbon monoxide C = 2-96 + 000032 V concentration C (ppm) + 00000005 V2 (3 h period) Nitric oxide concentration 7V = 46-9-0036Γ N Og/m3) (1 h period) + 000004Γ2 3 Smoke level S Og/m ) s = 9-49 + 0022 V (3 h period) L = 0000249P Lead concentration L + 00431 Og/m3) (3 h period)

V = total number of vehicles passing in 3 h period T = hourly traffic flow V = total number of vehicles in 3 h period p = total number of petrol-engine vehicles in 3 h period

areas. Tunnelling, while expensive, permits land to be developed without interference or areas to be left undisturbed. Severance due to transport facilities may leave isolated parcels of land in a non-conforming use situation leading to dereliction. Pedestrians are the most affected by severance making it difficult to cross heavy streams of traffic and causing not only danger but delay. The overall effect on the aggregate delay caused by different schemes should be used as one of the criteria of environmental evaluations.

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The incompatibility of pedestrian and vehicular environments is obvious, both from a consideration of amenity and for safety reasons. In many respects the pedestrian has been neglected in design, and certainly in cost-benefit analysis, and it is right that they should be considered more favourably than other groups of traveller. Visual Intrusion There are two broad groups of factors causing visual intrusion. The first is due to the construction of roads and buildings and the impact such works have on an observer will be strongly affected by the context in which they are placed. Superimposed on this static-built environment is that caused by the movement of people and vehicles. Much of the movement is transitory, for instance the incidence of large vehicles on the patterns of movement over time, and the effects of parked and loading vehicles must also be taken into account. Such other factors as the compatibility of age and style of buildings, their surface textures, layout, functions, accesses and the observer's position will all intrinsic­ ally interact with the subjective assessment of intrusion. Visual ex­ perience is like noise; some is pleasant, but perhaps for only a limited period or at a defined time. Finally, what is acceptable to one person or group may not be to others, or only in varying degrees. One method which has been used for visual assessments is based on a measurement of the solid angle subtended by a new structure from points of observational interest. The unit used is the steradian, defined as the angle subtended at the centre of a sphere of unit radius by unit surface area. For any point the total solid angle is 4π steradians. Because the method has not been correlated with responses the measures of solid angles have been grouped into three categories of slight, noticeable and marked. Measurements of solid angles can be made by counting the squares of equivalent area on an overlay designed to fit over a 180° photograph which has the new structure drawn on it; alternatively, a specially designed calculator can be used to trace out the structure. Generally the method is far from suitable because equal solid angles may embrace opposite results, e.g. Westminster Abbey and a coal tip, buildings inserted on a background of existing buildings

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and the movement of traffic, or parked vehicles, may be more disturbing than static intrusions. Visual intrusion also rapidly increases with height of structure, and the effect is more marked in rural than urban areas. Attitudinal surveys using photographic overlays or scenes pro­ jected onto a screen behind a window have also been used as ranking methods, but correlations are often found to be spurious or misleading, e.g. the proportion of blue sky or greenery in the picture may be the strongest influence. However, enough is known to improve the quality of design, although account must be taken of the situation of the viewer, i.e. whether from a moving vehicle, as a pedestrian or the outlook from a window, with each situation requiring the application of different design criteria. Besides the raising of aesthetic quality there are many ways of reducing the visual impact of roads and vehicles, both stationary and moving, through landscaping and subtle use of earth moulding, but the most important factors are the interrelationships between the individual parts of the built environment and the scale of components relative to each other. Both landscape and townscape must be seen as a total concept, each component interacting with the whole and, as an entity contributing to the overall enhancement of a specific environment. Discomfort and visual disturbance can be caused by a flicker of vehicle lights at night, both to pedestrians and residents. Similar problems arise from street lighting by the high levels of luminance provided on major routes. Conformity and compatibility between landusers ensures that conflicts are lessened, if not resolved. Construction Works Often the worst environmental deterioration will arise during con­ struction work from noise, dust, vibration, fumes, visual intrusion and severance, aspects of which are contained in the Control of Pollution Act 1974. By operational planning of the work to suit seasonal phasing and the careful timing of operations, some of the worst effects can be ameliorated. The pre-contract work entails predicting the likely levels of environmental disturbance and the identification of sensitive areas where monitoring may be needed during construction work. Protective

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Traffic Planning and Engineering

measures will require specifying and so will the mode of measurement. For instance, noise levels of 85 dB(A) occur at site boundaries from earth-moving plant and noise levels are based on L e q recommendations. While reductions of 6-10 dB(A) can be achieved by detailed schedul­ ing of the operation of plant combinations, silencers are relatively cheap to install on plant and reduce source noise by about 5 dß(A). In some instances only the erection of barriers, with reductions of about 10 to 12 dB(A), is effective unless earth moving is carried out by conveyor systems. Provision can be made at the design stage for earth mounding by contouring finished ground surfaces which form a permanent feature, not only reducing noise levels by up to 12 dB(A) if of suitable height, but forming a desirable visual feature for landscape treatment. An index (PANDLE) of noise and dust disturbance (Ps) caused by earth-moving plant along 100 m lengths of site has been developed by T R R L ( L R 7 5 2 ; 1977): Ps =

nsvsx\0~«,

where ns represents the number of dwellings within 100 m of the site fence over a length of 100 m and vs is the amount of earth being trans­ ported past the mid-point of each section as calculated from the mass haul diagram. Other Factors The control of commercial vehicles in residential and pedestrian areas is environmentally essential. The most cost-effective method is to prevent entry except for access in residential zones. This method is superior to peak-hour controls as it only involves rerouteing of through journeys and, overall, yields equivalent environmental benefits. The use of 24 h controls are expensive because alternative means of delivery have to be provided, usually necessitating break bulk depots and the use of a separate vehicle fleet. However, the latter method is often worth while in pedestrianised central areas, redevelopment areas and new towns. The Heavy Commercial Vehicles (Controls and Regulations) Act 1973 requires local authorities to survey, consult and prepare local

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lorry plans not only to improve amenity but to preserve it. Restricted vehicles are classified by maximum gross weights (7i, 11, 16 and 24 tons). An important control difficulty is the variable response from individuals of the relative nuisance attached to more frequent journeys of smaller vehicles compared to fewer heavier vehicles. It has been shown that a relatively large group of the population is more disturbed by the division of a 20 ton load into five vehicle loads of 4 tons than the original single load, but obviously circumstances vary depending on such factors as the type of load, the time of day and the nature of the road system. The problem is not confined to urban areas: increas­ ingly large vehicles use access roads to farms in isolated rural areas and are essential for the viability of agriculture. A national lorry routes network has, however, been established. Present use is advisory for vehicles of 16 ton weight, but it may become compulsory (except for access) when the major road network is completed, i.e. all motorways and 12,000 km of improved primary roads. The main problem remains in urban areas, and the use of positive signing for heavy vehicle routes and more information to drivers is advantageous in reducing the use of unsuitable roads. Dangerous loads are increasingly carried in large road vehicles and present considerable hazards. New methods of vehicle "tagging" are available by fitting transponders, giving a discrete identity to each vehicle, that can be interrogated by radio links. If a mishap occurs a computer program can identify the means and manner of dealing with the situation and also direct the necessary emergency vehicles to the scene, located from the last transmission. Environmental Impact Assessments The factors described above that contribute to environmental disbenefits, have to be assessed within a comprehensive evaluation frame­ work for a project. It is not only large projects that need to be assessed: it is more than likely that a small-scale undertaking in a particularly sensitive environment may be far more vital environmentally than the aggregate effects of larger works elsewhere. Procedures for dealing with environmental impacts have been developed in a number of countries,

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particularly in the United States, but with varying degrees of success and extensive resort to law suits. Under the National Environmental Policy Act of 1969 the procedures laid down in the United States include impact statements based on the proposals, the likely resulting pollution, alternatives to proposed action, the local short- and long-term position and resource commitments involved. Similar proposals for the appraisal of significant projects are likely to be introduced in the United Kingdom, making use of the experience of other countries. Wherever possible quantitative methods are preferred but where the techniques are not available subjective methods are acceptable provided that the qualitative approach is factual, cogently set down and exhaust­ ively argued. Some subjective forms of quantification have been found misleading in practice. Tabular presentations of the alternatives, "balance sheet" and matrix methods are sometimes appropriate, although the necessity to assign values and multipliers can introduce uncontrolled bias. Public participation is a necessary part of the con­ sultation process but, again, bias can result from the influences exerted by articulate pressure groups. FURTHER READING BROCH, J. T. (1969) Application ofB & K Equipment to Acoustic Noise Measurements, Bruel and Kjaer, Copenhagen. BUCHANAN, C. and CROMPTON, D. H. (1968) Objectives of traffic management, Traff. Engng Control 10 (1). BUCKLER, P. A. (1973) Stevenage superbus experiment, 4th Symp, Promoting Public Transport, Universityxof Newcastle. BUILDING RESEARCH STATION (1971) Motorway Noise and Dwellings, Dept. of the Environment Building Research Station, Digest 135. BUILDING RESEARCH STATION (1976) Predicting Road Traffic Noise, Building Research Establishment Report, HMSO, London. BURT, M. E. (1972) Roads and the Environment, TRRL Report LR 441, Transport and Road Research Laboratory. CHAPMAN, R. A., GAULT, H. E. and JENKINS, I. A. (1976) Factors Affecting the

Operation of Urban Bus Routes, Transp. Operations Res, Group, WP 23, Univ. Newcastle upon Tyne (see also WPs 8, 15 and 18). CHU, C. (1972) Environmental Effects of Urban Road Traffic, CES Info. Paper 26, Centre for Environmental Studies. COLVVTLL, D. M. (1973) Atmospheric Pollution from Vehicle Emissions: Measurements in Reading, 1971, TRRL Report LR 541, Transport and Road Research Laboratory.

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DELANEY, M. E. et al. Propagation of Traffic Noise in Typical Urban Situations, NPL Acoustics Report AC 54, National Physical Laboratory. DEPARTMENT OF THE ENVIRONMENT (1972) New Housing and Road Traffic Noise— Design Guide for Architects, Design Bulletin 26, HMSO, London. DEPARTMENT OF THE ENVIRONMENT (1975) Memorandum: Calculation of road traffic noise, HMSO, London; Also HM Government Statutory Instruments (1975) The Noise Insulation Regulations. DEPARTMENT OF THE ENVIRONMENT/WELSH OFFICE (1975) Calculation of Road Traffic

Noise, HMSO, London. DEPARTMENT OF THE ENVIRONMENT (1976) Traffic in General Improvement Areas, Note 9.297, HMSO, London. DIECKMANN, D. (1958) A study of the influence of vibrations on man, Ergonomics 1(4). FISHER, C. H. (1969) Petrol engine emissions—what next? Automobile Engr., April. GREATER LONDON COUNCIL. Traffic Noise, Greater London Council, 1966; and Traffic Noise, Major Urban Roads, Urban Design Bulletin No. 1, 1970. HARLAND, D. G. and MARTIN, D. J. (1977) The Prediction of Noise from Road Con­ struction Sites, TRRL Report LR 756, Transport and Road Research Labora­ tory. HAYNES, C. D. and SOUTH ALL, M. (1968) Atmospheric Pollution from Petrol Engines, Motor Industries Research Association Report No. 1968/5. HEGGIE, I. G. (1975) Priority Innovation and Restraint: Some Empirical Evidence, WP 2, Oxford Univ. Transp. Studies Unit. HODGKINSON, D. Η. and WARREN, G. (1976) Public participation and environmental management (in Traffic and Environmental Management) PTRC Annual Meeting, Warwick. HOPKINSON, R. G. (1972) The evaluation of visual intrusion in transport situations, Traff. Engng Control 14 (8). HOUSE, M. E. (1973) Traffic induced vibration in buildings, / . Instn Highway Engrs, xx (2). HOUSE OF COMMONS (1974) Control of Pollution Act 1974, HMSO, London. JOHNSON, D. R. and SAUNDERS, E. G. (1968) The evaluation of noise from freely flowing road traffic, / . Sound Vibr. 7 (207). KERENSKY, O. A. (1968) Urban Motorways and their Environment, Rees Jeffreys Triennial Lecture, Town Planning Institute, London. LANDAU, A. G. (1968) Distances between stops on transport services minimising travel times, Proc. 4th Int. Symp. on Theory of Traff. Flow, Karlsruhe. LANGDON, F. J. and SCHOLES, W. E. (1968) The Traffic Noise Index: a Method of Controlling Noise Nuisance, Building Research Station Current Paper 38/68; and Subjective Response to Road Traffic Noise, BRS Current Paper 37/68. LASSIERE, A. (1976) The Environmental Evaluation of Transport Plans, Res. Report 8, Department of the Environment, HMSO, London. LEONARD, D. R. (1966) Human Tolerance Levels for Bridge Vibrations, RRL Report LR 34, Road Research Laboratory. LESLEY, L. J. S. (1976) Optimum bus-stop spacing, Traff. Engng Control 17 (10 and 11). LEWIS, W. A. and PARSONS, A. W. (1973) The application of belt conveyors in road earthworks, Proc. Instn Civ. Engrs 54 (8). MALTBY, D., MONTEATH, I. G. and LAWLER, K. A. (1975) Energy considerations in TPE - K

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urban transport planning, Proc. Seminar, PTRC Annual Meeting, Warwick, Planning and Transport Research and Computation Ltd., London. MAYCOCK, G. (1971) Implementation of traffic restraint, Symp. on Traffic Restraint, Instn. Highways Engrs., April. MILLAR, A. and COOK, J. A. (1968) Pedestrians and Vehicles on Housing Estates: a User Study, Building Research Station Current Paper No. CP 23/68. MILLARD, R. (Chairman) (1970) A Review of Road Traffic Noise, The Working Group on Research into Road Traffic Noise, R R L Report LR 357, Road Research Laboratory. MINISTRY OF TRANSPORT. Urban Traffic Engineering Techniques, HMSO, 1965. Traffic Management and Parking, 4.134 Circular, 1969. Traffic and Transport Plans, Roads Circular 1/68. MINISTRY OF TRANSPORT (1967) Cars for Cities—a Study of Trends in the Design of Vehicles with Particular Reference to their use in Towns, HMSO, London. MINISTRY OF TRANSPORT (1970) Roads for the Future: the New Inter-urban Plan for England, Cmnd. 4369, HMSO, London. MITCHELL, G. B. and SPILLER, B. E. (1974) The Harlow dial-a-ride experiment, Proc. 1st UK Dial-a-Ride Symposium, Cranfield Institute of Technology, Cranfield. NATIONAL SOCIETY FOR CLEAN AIR (1967) Air Pollution from Road Vehicles, Report by the Technical Committee of the National Society for Clean Air, London. NELSON, P. M. (1975) A Computer Model of Traffic Noise to Solve Planning Problems, OECD. OECD (1975) Streets for People, OECD. O'LEARY, J. D . (1969) Evaluating the environmental impact of an urban expressway, Tr. Quart. July. OLIVER, W. T. (1968/9) Practical emission control systems—air injection into exhaust manifold, Proc. Instn Mech. Engrs 183 (3E). PAGE, E. W. M. and SEMPLE, W., Silent and vibration-free sheet pile driving, Proc. Instn Civil Engrs 41, 19. PTRC (1975 and 1976) Public transport, Proc. Sem. Annual Meeting, Warwick; also Traffic and environmental management. REED, L. E. and BARRETT, C. F. (1965) Air pollution from road traffic—measure­ ments in Archway Road, London, Int J. Air Water Poll. 9. REED, L. E. (1973) Environmental pollution, Paper No. 6 at 100th Annual Conference, Instn of Municipal Engineers. RIDLEY, G. (1973) Bus lanes in London, J. Instn Highway Engrs xx (7). ROBINSON, D. W. (1969) The Concept of Noise Pollution Level, Ministry of Tech­ nology, NPL, Aero Report AC 38. SHERWOOD, P. T. and BOWERS, P. H. (1970) Air Pollution from Road Traffic—A Review of the Present Position, R R L Report LR 352, Road Research Laboratory. THE NOISE ADVISORY COUNCIL (1972) Traffic Noise: The Vehicle Regulations and their Enforcement, HMSO, London. TRANSPORTATION

RESEARCH

BOARD.

Transportation

for

Elderly,

Disadvantaged

and Handicapped People in Rural Areas, Record 578. Transportation Environmental Review Process, Record 580. Innovations in Transportation Systems Planning, Record 582. TROTT, J. J. and WHIFFIN, A. C. (1965) Measurements of the axle loads of moving vehicles on trunk roads, Roads and Road Constr. 43 (511). VARIOUS. Traffic Management, Proc. PTRC Seminar, 1971; and Traffic Management,

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Proc. PTRC Seminar, 1973, Planning and Transport Research and Computation Co. Ltd. WALLER, R. A. (1967) Environmental Quality, its Measurement and Control, Int. Symp. on Urban Renewal, Brussels. WATKINS, L. H. (1972) Urban Transport and Environmental Pollution, TRRL Report LR 455, Transport and Road Research Laboratory. WEBSTER, F. V. (1971) Priority to Buses as Part of Traffic Management, TRRL Report LR 448, Transport and Road Research Laboratory. WEEB, J. (1973) Noise studies related to motorway alignment, /. Instn Highway Engrs xx (5). WHITTIN, A. C. and LEONARD, D. R. A Survey of Traffic-induced Vibrations, RRL Report LR 418, Building Research Station. Cracking in Buildings, BRS Digest No. 75 (1966); Vibrations in Building—\ and 2, BRS Digest Nos. 117 and 118 (1970), Building Research Station, HMSO, London. WILSON, SIR ALAN (Chairman) (1963) Noise, Final Report of the Committee on the Problem of Noise, Cmnd. 2056, HMSO, London.