- Email: [email protected]
Traffic control systems to alleviate congestion and air pollution
the Science o f the Total Environment 4a, I n w ~ l c u l i ~ the ~ n ~ n l
ELSEVIER
Iom'ul fo~ ~ Lemlll¢ h ~ h I ~ In [ t l l l ~ n l h i p w ~ MIn
The Science of the Total Environment 146/147 (1994) 45-50
Traffic control systems to alleviate congestion and air pollution A. Monz6n de Cficeres Departamento de Transportes, E. T.S. 1. Caminos, Canales y Puertos, Ciudad Universitaria s/n, 28040 Madrid, Spain
Abstract After underlining the importance of the environmental problems that arise from the increase of traffic levels in cities, and re-examining the main consequences and possibilities for their improvement, some experiments carried out in Barcelona are set out. The introduction of an intelligent traffic control system in a congested area of the city has brought substantial improvements in traffic conditions and significant reductions of fuel consumption and emission of atmospheric pollutants. Future possibilities for systems based on traffic control are emphasised in order to improve their environmental consequences. Key words: Traffic control; Pollution; Congestion; Urban traffic
1. Problems derived from traffic in cities The present population clearly tends to live in the cities. This has entailed an exponential growth of urban areas, which take in the majority of the population (at present over 70%). The possibilities for growth of the cities have been increased by the growth of the motor park, up to such a point that, at present, big cities could not operate without mechanical means of transport. In turn, just as the growth of cities has been made possible thanks to the motor vehicle and to collective means of transport, their growth is bringing about the collapse of the system they have helped develop. The damaging effects arising from the intensive use of the motor vehicle have caused adverse reactions, especially in the historical central areas of the cities. According to Nijkamp [1] there is no linear relationship between the supply of infrastructures and
i
Intensity
t rartsport/con-anunications
Fig. 1. Relationship between quality of life and transport infrastructures. means of transport and the quality of life. as shows the graph in Fig. 1. The adverse effects due to the high levels of urban mobility can be summed up in the following: •
0048-9697/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved. SSD1 0048-9697(93)04095-Q
congestion: with losses caused by an increase of the travelling time, operative costs, major
46
•
•
•
A. Mon:6n de C(tceres / Sci. Total Environ. 146/147 (1994) 45-50
soil occupation and lack of efficiency of the transport system. air pollution: the high amount of gases proceeding from the emission of waste gases by motor vehicles causes certain levels of concentration of solid and gaseous elements, which are injurious to living beings and bring about losses of the quality of life and damage to property [2]. noise and vibrations: the contact between wheel and pavement and the engine functioning lead to noise and vibrations, which are sensed by the local populations along the communication routes and end up affecting their labour activities, rest, etc. delays, risks of accidents: this group of effects includes accidents to pedestrians and drivers and the effects of crossings on the big arteries, which bring about delays for pedestrians.
This group of negative effects has increased pressure on politicians and agents at all levels. Thus, on the part of the EU, there has been an important change to attitude in the last few years. First, there is the Single Act; since its passing, environmental politics have acquired naturalisation within common politics. In addition to the numerous policies and recommendations of a specific nature that have been passed in recent years, it seems worthwhile to take a closer look at some recent documents of a general nature that have been sent out by the Commission. We could, for example, refer to the Green Book of the Cities. This is a document calling attention to ways of approaching the solution of the problems of big urban agglomerations in order to protect the environment and the quality of life. More recently, the Communication of the Commission, called 'Green Paper', has been passed, which deals with "The Impact of Transport on the Environment: a common strategy for a 'sustainable mobility' ". In this document, the importance of the damaging effects of transport in the member countries is underlined with comparative statistics. Together with this description, it is taken into consideration that the construction of the common Europe is leading to an exponential increase of mobility. This increase has a double cause: on the one hand, the elimination of barriers
between the member countries has engendered a multitude of relationships (commercial, cultural, research, leisure, etc.) that were of less importance previously; on the other hand, the period of economic growth of the last decade has also brought a widespread increase of motorisation rates and of the demand for mobility. Moreover, the free market philosophy, which is one of the 'rules of the game' of the Single Market, of the European Economic Area and of the Monetary Union, will create more mobility, it being estimated that within the next 20 years traffic in all intra-European relationships will have doubled [3]. The solutions to the problems, according to the Green Paper, will have to come from a general viewpoint, by integrating transport in the goals of 'sustainable development', and in order for that development to be genuine, it must be compatible with the maintenance of certain standards of environmental quality. In that sense, the document advocates 'sustainable mobility' as a goal. This means that solutions must be found to the areas of conflict between transport and environment, and these solutions must take into consideration the agreement among the member countries on environmental quality levels - - noise, emissions into the atmosphere, etc. - - so as to be able to apply common measures without affecting the competitivity of companies located in each of the countries.
2. Urban traffic control strategies It is generally agreed that the solutions have to allow for the adaptation of the road network to what is usually called its 'environmental capacity'. This capacity will depend on the characteristics of the infrastructure itself, on the urban area where it is located, on its environmental conditions and on the traffic it is used by. The first two are related with the infrastructure, which is why their modification is difficult and costly, especially when we are dealing with consolidated urban areas. The solutions concerning infrastructures aim at reducing the speed of circulation and indirectly dissuading people from the use of certain roads. This can be achieved by obstacles on the road (road humps, rumble strips)
A. Monz6n de Okceres / Sci. Total Environ. 146/147 (1994) 45-50
or by special designs which force the driver to reduce speed [4]. This kind of solution is being adopted in residential areas in many European countries, especially in the most advanced ones. An example of these actions are the ~zones 30' which include a wide range of procedures of 'traffic calming'. There are also urban planning solutions directed towards avoiding negative environmental effects in the most sensitive areas: near schools, hospitals, and in residential areas [5]. The possibilities for action in relation to natural environmental conditions are few. It is well known that the pollutant concentration largely depends on rainfall with wind, which depends on the climatology and topography of the area. What man can do - - and has been doing for some time in this respect is to facilitate dispersion through the design and location of the centres of emission: factory chimneys, gas exhausts, etc. If these are located in areas with strong air turbulence and outside cities, the negative effects will be less intense. The third group of measures, which this paper will focus on, refers to the possibilities of applying measures of urban traffic control. Those measures directed towards an optimum modal distribution will be ignored, as they are not within the reach of this paper. We can analyse these measures in terms of three conceptual groups. -
-
2.1. Restrictions on using cars The most drastic way of solving the negative effects of traffic in cities is by suppressing it. This procedure has been applied in many historical central urban areas of European cities. In many of them, important areas of the urban centre have been totally closed to vehicular traffic. In other cases, the restriction has been partial, affecting only certain arterial roads that have been converted into pedestrian roads. This procedure solves the traffic problems, but it also brings about serious difficulties for the mobility of the residents of those areas, for shops and all kinds of installations (hospitals, offices, schools, etc.), which also entails important social costs. Another possibility is to limit the number of vehicles that can use a certain area. There is a wide range of possibilities: restriction by the registration number, odd or even, according to the days of
47
the week; indirect restrictions by parking prohibition; or monetary measures which may tax parking in certain areas or, more directly, circulation through the city centres (road pricing). The introduction of these, more flexible, systems requires a series of expenses for their installation and for the surveillance of the observance of the rules. However, the difficulties of the rigidity of the aforementioned system are avoided. 2.2. Speed limitation The pollutant emissions, as well as noise and other adverse effects, are directly related to the speed of the vehicles. During the years of the oil crisis, in Spain and other Western countries~ speed limits were introduced for traffic on interurban roads in order to lower the energy bill. Later, these kinds of measures were extended for reasons of road safety, as the standards of road quality increases. In the cities, speed is also limited, but it is very difficult to control its observance, for technical and operative reasons. As a consequence, the only limitation which has really been operating in the urban environment is the one imposed by congestion, which has caused the average speed in big cities to fall very significantly in recent years. However, in the outlying residential areas, without significant traffic, the high speed of the vehicles produces adverse effects, especially with regard to road safety. In some countries, designs have been developed to reduce speed, as previously mentioned. Whether it is by these procedures, or by control through traffic lights, which prevent long runs without stops, or by the simple and traditional speed limit, the areas of ~traffic calming' where the speed is reduced have been spreading since they were started in the 1970s [6]. Studies in areas of several locations seem to show that the appropriate speed limit to achieve the best overall effects of efficiency, security and environmental improvement is of 30 km/h [7]. 2.3. Optimising the use of infrastructure by control systems It is obvious that the most adverse situations, from an environmental point of view, occur when there is an important mismatch between the demand (traffic level) and the available infrastruc-
48
A. Monz6n de C6ceres / Sci. Total Environ. 146/147 (1994) 45-50
tures. At low speed, congestion increases and so do noise and pollution. The third group of measures that can be introduced is to apply systems which can allow users to avoid the points of peak demand in both space and time. This principle is fundamental to extensive research and development programmes which are aimed at homologatng systems to improve the efficiency of the system [8]. It is the goal of the EU programme DRIVE, which is at its second stage of applied research and standardisation of systems. The possible applications aim at providing the driver with more information, so that she can adapt her journey to the capacity of the infrastructure, either by using alternative routes or by giving her information in real time about the travelling conditions that allows her to decide whether to travel or not, whether to change the hour, etc. All possibilities of DRIVE and other cooperative programmes like P R O M E T H E U S are within a new conceptual frame for traffic engineering that has been called IRTE (Integrated Road Transport Environment), i.e. an integrated approach to transport and infrastructures. Nevertheless, although there are many programmes that promise good mid-term applications, there are still no operative systems on a commercial level which can quantify the results to be expected. At present there are several projects at the stage of pilot studies, which will make possible the introduction of these systems within the next few years.
In the early 1980s, a series of measures were introduced into the systems of traffic lights control, consisting of the modernisation of control computers and of including systems ofcentralised control [9]. After the new system had been introduced, the results of the application of three alternative plans for controlling 49 intersections by traffic lights, and directed by the computer of that area, were evaluated during a week. The three alternatives evaluated were the following. •
•
•
3. Environmental consequences of the introduction of an expert system of traffic regulation At a local level, we can describe some concrete experiments which produced encouraging results for the possibility of improving pollution levels by applying intelligent systems of traffic control.
Fixed stages: this was the old control system, consisting of only one regulation schedule operating all day with the same time intervals. This is a system without any flexibility. Fixed control plans: this system applies a series of alternative control plans, stored in the memory of the area computer, and at the same time allows any damage or failure at any of the intersections to be located. In this case, there were four control plans available, which were alternated during the day at ten prefixed time intervals. One of them was applied during night hours, another one at off-peak hours, and the last two in different situations at the peak hours. Dynamic system: in this case the computer applies the optimum control plan according to the traffic data it receives. The calculation of the variables of the control plan is based on the traffic load, elaborated from the data supplied by the detectors about every 5 min. The schedule applied by the central computer is thus adjusted at each interval, and a dynamic process of adaptation to the optimum cycle for the real traffic situation at each moment is established.
The results obtained are shown in Table 1. As can be deduced from the overall results in Table 1,
Table 1 Percentage variation of the economic and environmental effects with different traffic control systems in the South area of Barcelona
Total travelling times Fuel consumption Pollutant emission
Fixed stages
Fixed control plans
Dynamic system
100% 100% 100%
86% ( - 14%) 88.5% ( - 11.5%) 88.4°/,, (-11.6'¼,)
81% ( - 19%) 83.5% ( - 16.5%) 82.8"/0 (-17.2%)
A. Monz6n de Chceres / Sci. Total Environ• 146/147 (1994) 45-50
49
Table 2 Fuel consumption and pollutant emissions associated with the average traffic flow (0.525 veh × km/h) in the Sout area of Barcelona
Petrol (1 × veh/h) Diesel oil (1 × veh/h) Particles (kg × veh/h) SO 2 (kg × veh/h) N 2 (kg × veh/h) Hydrocarbons (kg x veh/h) CO (kg x veh/h)
Fixed stages
Control plans
Dynamic system
918 962 12.87 5.17 35 34.7 236
821 (89%) 848 (88%) 11.27 (88%) 4.50 (87%) 31 (89%) 30.9 (89%) 211 (89%)
771 (84%) 794 (83%) 10.55 (82%} 4.24 (82%) 29 (83%) 28.9 (83%) 198 (84%)
the main improvement is achieved in travelling time. The abatement of atmospheric pollution and energy consumption turns out to be slightly less. Another conclusion is that the step from a totally fixed system of traffic light stages to a centralised system of fixed control plans is the improvement which produces most benefits• The following step, from a system of control plans to a dynamic system, provides benefits of 50% of those achieved by the first step. We can therefore state that the application of centralised systems that allow for the application of different plans, brings an improvement, in all aspects, of over 11% and that the introduction of intelligent systems of a dynamic nature allows to increase this improvement of over 16%. In addition to a detailed study on the improvement in travelling time, which cannot be dealt with here, the reductions of energy consumption and pollutant emissions were analysed in detail• As a reference we will state that the percentage of heavy vehicles in the streets of the area was between 11% and 22%, which is fairly high for an urban area. The estimation of consumption and emissions was based on an existing study [10]. The various means were taken from average vehicles in the following positions [10]: (a) stopped position; (b) stable speed; (c) acceleration; and (d) deceleration• The measurements that were carried out have been correlated with the gauged traffic flow. The results of each kind of fuel and for each of the pollutants considered are shown in Table 2. It can be seen that consumption and pollutant emissions, considered separately, do not vary significantly from the overall average values shown in Table 1, i.e. the percentage improvements are similar for all kinds of pollutants considered.
The improvements also record another important result: that improvements of mobility are related to environmental improvements and reduction of energy consumption. This shows that the group of measures directed towards optimising the use of infrastructures through more efficient traffic
NO 2 EMISSIONS ','.. '.
.. -
".
fixed stages f i x e d schedules dynamic system
°,,,.,o,~
..... i.,o ~.~°°,
x ',
•
".•
• •
+ x
.
i..p°.30J~
kg " veh/hour CO~ EMISSIONS
f ~ e d stages f ~ e d schedules dynamic system ,00••,°L.
~°0M0]'
J=
',
!!i!i~!ii!
•.
",,
; !~!ii~iZ!! 1,,.0616 1,.,,~,,
'...
,,0.,J,.
,,°•.,,~
~,0.~lu ,,0.~,,,
•"
i,~.0°,~
~,~•t~,,
,~,.~,.
• •
,~o.,.,~ ~ , J . , ~ kg " veh/hour
Fig. 2. Relationship between air pollutant emissions and the traffic level.
50 control systems p r o d u c e s positive results in the three previous fields. These results, a n d o t h e r similar results o b t a i n e d in o t h e r cities, suggest that m a j o r i m p r o v e m e n t s can be achieved by a p p l y i n g the field o f t e l e c o m m u n i c a t i o n s to the t r a n s p o r t sector [11]. In o r d e r to c o m p l e t e the assessment o f the results obtained, an analysis was carried out o f the variation o f each o f the emissions with different levels of traffic, a c c o r d i n g to several routes established in the area o f study. The results o b t a i n ed, together with the d a t a from the survey and their extrapolation, after a regression analysis o f each variable with the traffic d e m a n d , for which values for r 2 o f over 0.7 were o b t a i n e d , are shown in Fig. 2.
4. Conclusions The experiments show the possibilities o f the direction a d v o c a t e d by the E U C o m m i s s i o n o f applying expert traffic c o n t r o l systems and thus diminishing the p r o b l e m s o f congestion a n d the associated negative e n v i r o n m e n t a l effects. T o g e t h e r with the measures o f traffic restriction in those areas where the m i n i m u m level is far exceeded, there are great possibilities in intelligent systems that a d a p t the d e m a n d to the 'environmental c a p a c i t y ' o f infrastructures. F r o m the results we can e x t r a p o l a t e that, within certain levels o f traffic, we can aim at optimising the objective o f m a x i m u m fluency in o r d e r to reduce congestion and its negative effects. T h a t is why it
,4. Monz6n de C6ceres / Sci. Total Environ. 146/147 (1994) 45-50
is essential to invest in the d e v e l o p m e n t o f efficient technical systems a n d in their i n t r o d u c t i o n into the cities, first at a pilot stage, to be able to a p p l y them on a general scale later.
5. References 1 Nijkamp P,, Urban traffic restrain measures: a road to success? In: Conference on Improving Traffic and Quality of Life in Metropolitan Areas. Council of Europe, Strasbourg, 1990. 2 Calder6n E., Trfifico Urbano y Medio Ambiente: un Ensayo de Planificaci6n Conjunta. Instituto de Estudios de Planificaci6n. Madrid, 1975. 3 PROGNOS, Development of Freight Transport in Europe. TTC, MTTC. Madrid, 1989. 4 Hills P. et al., Roads and Traffic in Urban Areas. Institution of Highways and Transportation. Department of Transport. HMSO. London, 1987. 5 Monz6n A., Impactos Ambientales de Carreteras. Carreteras, Vol. 47. Madrid, 1990. 6 Keller H.H., La Mod6ration de la Circulation en RFA. Actes du Congr6s 'Vivre et Circuler en Ville'. CETUR, Paris, 1990. 7 Mfiller P. et al., Bilanz zu Tempo 30. Grfine Reihe Nr. 11 des Fachgebiets Verkehrswesen. RFA, 1988. 8 Catling I., System convergence - - the potential for an integrated road transport environment. Transportation, 17 (1990) 285-299. 9 Ajuntament de Barcelona, Evaluaci6n del Sistema de Control de Trfifico del Area Sur. Servicio de Circulaci6n del Ayuntamiento de Barcelona, 1981. 10 MINER, Estudio y Diagn6stico de la Contaminacion Atmosf6rica en el Cintur6n Industrial de Barcelona. Madrid, 1981. 11 DRIVE, R & D in Advanced Road Transport Telematics in Europe, DRIVE'90. CED, DG Xlll, Brussels, 1990.
ELSEVIER
Iom'ul fo~ ~ Lemlll¢ h ~ h I ~ In [ t l l l ~ n l h i p w ~ MIn
The Science of the Total Environment 146/147 (1994) 45-50
Traffic control systems to alleviate congestion and air pollution A. Monz6n de Cficeres Departamento de Transportes, E. T.S. 1. Caminos, Canales y Puertos, Ciudad Universitaria s/n, 28040 Madrid, Spain
Abstract After underlining the importance of the environmental problems that arise from the increase of traffic levels in cities, and re-examining the main consequences and possibilities for their improvement, some experiments carried out in Barcelona are set out. The introduction of an intelligent traffic control system in a congested area of the city has brought substantial improvements in traffic conditions and significant reductions of fuel consumption and emission of atmospheric pollutants. Future possibilities for systems based on traffic control are emphasised in order to improve their environmental consequences. Key words: Traffic control; Pollution; Congestion; Urban traffic
1. Problems derived from traffic in cities The present population clearly tends to live in the cities. This has entailed an exponential growth of urban areas, which take in the majority of the population (at present over 70%). The possibilities for growth of the cities have been increased by the growth of the motor park, up to such a point that, at present, big cities could not operate without mechanical means of transport. In turn, just as the growth of cities has been made possible thanks to the motor vehicle and to collective means of transport, their growth is bringing about the collapse of the system they have helped develop. The damaging effects arising from the intensive use of the motor vehicle have caused adverse reactions, especially in the historical central areas of the cities. According to Nijkamp [1] there is no linear relationship between the supply of infrastructures and
i
Intensity
t rartsport/con-anunications
Fig. 1. Relationship between quality of life and transport infrastructures. means of transport and the quality of life. as shows the graph in Fig. 1. The adverse effects due to the high levels of urban mobility can be summed up in the following: •
0048-9697/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved. SSD1 0048-9697(93)04095-Q
congestion: with losses caused by an increase of the travelling time, operative costs, major
46
•
•
•
A. Mon:6n de C(tceres / Sci. Total Environ. 146/147 (1994) 45-50
soil occupation and lack of efficiency of the transport system. air pollution: the high amount of gases proceeding from the emission of waste gases by motor vehicles causes certain levels of concentration of solid and gaseous elements, which are injurious to living beings and bring about losses of the quality of life and damage to property [2]. noise and vibrations: the contact between wheel and pavement and the engine functioning lead to noise and vibrations, which are sensed by the local populations along the communication routes and end up affecting their labour activities, rest, etc. delays, risks of accidents: this group of effects includes accidents to pedestrians and drivers and the effects of crossings on the big arteries, which bring about delays for pedestrians.
This group of negative effects has increased pressure on politicians and agents at all levels. Thus, on the part of the EU, there has been an important change to attitude in the last few years. First, there is the Single Act; since its passing, environmental politics have acquired naturalisation within common politics. In addition to the numerous policies and recommendations of a specific nature that have been passed in recent years, it seems worthwhile to take a closer look at some recent documents of a general nature that have been sent out by the Commission. We could, for example, refer to the Green Book of the Cities. This is a document calling attention to ways of approaching the solution of the problems of big urban agglomerations in order to protect the environment and the quality of life. More recently, the Communication of the Commission, called 'Green Paper', has been passed, which deals with "The Impact of Transport on the Environment: a common strategy for a 'sustainable mobility' ". In this document, the importance of the damaging effects of transport in the member countries is underlined with comparative statistics. Together with this description, it is taken into consideration that the construction of the common Europe is leading to an exponential increase of mobility. This increase has a double cause: on the one hand, the elimination of barriers
between the member countries has engendered a multitude of relationships (commercial, cultural, research, leisure, etc.) that were of less importance previously; on the other hand, the period of economic growth of the last decade has also brought a widespread increase of motorisation rates and of the demand for mobility. Moreover, the free market philosophy, which is one of the 'rules of the game' of the Single Market, of the European Economic Area and of the Monetary Union, will create more mobility, it being estimated that within the next 20 years traffic in all intra-European relationships will have doubled [3]. The solutions to the problems, according to the Green Paper, will have to come from a general viewpoint, by integrating transport in the goals of 'sustainable development', and in order for that development to be genuine, it must be compatible with the maintenance of certain standards of environmental quality. In that sense, the document advocates 'sustainable mobility' as a goal. This means that solutions must be found to the areas of conflict between transport and environment, and these solutions must take into consideration the agreement among the member countries on environmental quality levels - - noise, emissions into the atmosphere, etc. - - so as to be able to apply common measures without affecting the competitivity of companies located in each of the countries.
2. Urban traffic control strategies It is generally agreed that the solutions have to allow for the adaptation of the road network to what is usually called its 'environmental capacity'. This capacity will depend on the characteristics of the infrastructure itself, on the urban area where it is located, on its environmental conditions and on the traffic it is used by. The first two are related with the infrastructure, which is why their modification is difficult and costly, especially when we are dealing with consolidated urban areas. The solutions concerning infrastructures aim at reducing the speed of circulation and indirectly dissuading people from the use of certain roads. This can be achieved by obstacles on the road (road humps, rumble strips)
A. Monz6n de Okceres / Sci. Total Environ. 146/147 (1994) 45-50
or by special designs which force the driver to reduce speed [4]. This kind of solution is being adopted in residential areas in many European countries, especially in the most advanced ones. An example of these actions are the ~zones 30' which include a wide range of procedures of 'traffic calming'. There are also urban planning solutions directed towards avoiding negative environmental effects in the most sensitive areas: near schools, hospitals, and in residential areas [5]. The possibilities for action in relation to natural environmental conditions are few. It is well known that the pollutant concentration largely depends on rainfall with wind, which depends on the climatology and topography of the area. What man can do - - and has been doing for some time in this respect is to facilitate dispersion through the design and location of the centres of emission: factory chimneys, gas exhausts, etc. If these are located in areas with strong air turbulence and outside cities, the negative effects will be less intense. The third group of measures, which this paper will focus on, refers to the possibilities of applying measures of urban traffic control. Those measures directed towards an optimum modal distribution will be ignored, as they are not within the reach of this paper. We can analyse these measures in terms of three conceptual groups. -
-
2.1. Restrictions on using cars The most drastic way of solving the negative effects of traffic in cities is by suppressing it. This procedure has been applied in many historical central urban areas of European cities. In many of them, important areas of the urban centre have been totally closed to vehicular traffic. In other cases, the restriction has been partial, affecting only certain arterial roads that have been converted into pedestrian roads. This procedure solves the traffic problems, but it also brings about serious difficulties for the mobility of the residents of those areas, for shops and all kinds of installations (hospitals, offices, schools, etc.), which also entails important social costs. Another possibility is to limit the number of vehicles that can use a certain area. There is a wide range of possibilities: restriction by the registration number, odd or even, according to the days of
47
the week; indirect restrictions by parking prohibition; or monetary measures which may tax parking in certain areas or, more directly, circulation through the city centres (road pricing). The introduction of these, more flexible, systems requires a series of expenses for their installation and for the surveillance of the observance of the rules. However, the difficulties of the rigidity of the aforementioned system are avoided. 2.2. Speed limitation The pollutant emissions, as well as noise and other adverse effects, are directly related to the speed of the vehicles. During the years of the oil crisis, in Spain and other Western countries~ speed limits were introduced for traffic on interurban roads in order to lower the energy bill. Later, these kinds of measures were extended for reasons of road safety, as the standards of road quality increases. In the cities, speed is also limited, but it is very difficult to control its observance, for technical and operative reasons. As a consequence, the only limitation which has really been operating in the urban environment is the one imposed by congestion, which has caused the average speed in big cities to fall very significantly in recent years. However, in the outlying residential areas, without significant traffic, the high speed of the vehicles produces adverse effects, especially with regard to road safety. In some countries, designs have been developed to reduce speed, as previously mentioned. Whether it is by these procedures, or by control through traffic lights, which prevent long runs without stops, or by the simple and traditional speed limit, the areas of ~traffic calming' where the speed is reduced have been spreading since they were started in the 1970s [6]. Studies in areas of several locations seem to show that the appropriate speed limit to achieve the best overall effects of efficiency, security and environmental improvement is of 30 km/h [7]. 2.3. Optimising the use of infrastructure by control systems It is obvious that the most adverse situations, from an environmental point of view, occur when there is an important mismatch between the demand (traffic level) and the available infrastruc-
48
A. Monz6n de C6ceres / Sci. Total Environ. 146/147 (1994) 45-50
tures. At low speed, congestion increases and so do noise and pollution. The third group of measures that can be introduced is to apply systems which can allow users to avoid the points of peak demand in both space and time. This principle is fundamental to extensive research and development programmes which are aimed at homologatng systems to improve the efficiency of the system [8]. It is the goal of the EU programme DRIVE, which is at its second stage of applied research and standardisation of systems. The possible applications aim at providing the driver with more information, so that she can adapt her journey to the capacity of the infrastructure, either by using alternative routes or by giving her information in real time about the travelling conditions that allows her to decide whether to travel or not, whether to change the hour, etc. All possibilities of DRIVE and other cooperative programmes like P R O M E T H E U S are within a new conceptual frame for traffic engineering that has been called IRTE (Integrated Road Transport Environment), i.e. an integrated approach to transport and infrastructures. Nevertheless, although there are many programmes that promise good mid-term applications, there are still no operative systems on a commercial level which can quantify the results to be expected. At present there are several projects at the stage of pilot studies, which will make possible the introduction of these systems within the next few years.
In the early 1980s, a series of measures were introduced into the systems of traffic lights control, consisting of the modernisation of control computers and of including systems ofcentralised control [9]. After the new system had been introduced, the results of the application of three alternative plans for controlling 49 intersections by traffic lights, and directed by the computer of that area, were evaluated during a week. The three alternatives evaluated were the following. •
•
•
3. Environmental consequences of the introduction of an expert system of traffic regulation At a local level, we can describe some concrete experiments which produced encouraging results for the possibility of improving pollution levels by applying intelligent systems of traffic control.
Fixed stages: this was the old control system, consisting of only one regulation schedule operating all day with the same time intervals. This is a system without any flexibility. Fixed control plans: this system applies a series of alternative control plans, stored in the memory of the area computer, and at the same time allows any damage or failure at any of the intersections to be located. In this case, there were four control plans available, which were alternated during the day at ten prefixed time intervals. One of them was applied during night hours, another one at off-peak hours, and the last two in different situations at the peak hours. Dynamic system: in this case the computer applies the optimum control plan according to the traffic data it receives. The calculation of the variables of the control plan is based on the traffic load, elaborated from the data supplied by the detectors about every 5 min. The schedule applied by the central computer is thus adjusted at each interval, and a dynamic process of adaptation to the optimum cycle for the real traffic situation at each moment is established.
The results obtained are shown in Table 1. As can be deduced from the overall results in Table 1,
Table 1 Percentage variation of the economic and environmental effects with different traffic control systems in the South area of Barcelona
Total travelling times Fuel consumption Pollutant emission
Fixed stages
Fixed control plans
Dynamic system
100% 100% 100%
86% ( - 14%) 88.5% ( - 11.5%) 88.4°/,, (-11.6'¼,)
81% ( - 19%) 83.5% ( - 16.5%) 82.8"/0 (-17.2%)
A. Monz6n de Chceres / Sci. Total Environ• 146/147 (1994) 45-50
49
Table 2 Fuel consumption and pollutant emissions associated with the average traffic flow (0.525 veh × km/h) in the Sout area of Barcelona
Petrol (1 × veh/h) Diesel oil (1 × veh/h) Particles (kg × veh/h) SO 2 (kg × veh/h) N 2 (kg × veh/h) Hydrocarbons (kg x veh/h) CO (kg x veh/h)
Fixed stages
Control plans
Dynamic system
918 962 12.87 5.17 35 34.7 236
821 (89%) 848 (88%) 11.27 (88%) 4.50 (87%) 31 (89%) 30.9 (89%) 211 (89%)
771 (84%) 794 (83%) 10.55 (82%} 4.24 (82%) 29 (83%) 28.9 (83%) 198 (84%)
the main improvement is achieved in travelling time. The abatement of atmospheric pollution and energy consumption turns out to be slightly less. Another conclusion is that the step from a totally fixed system of traffic light stages to a centralised system of fixed control plans is the improvement which produces most benefits• The following step, from a system of control plans to a dynamic system, provides benefits of 50% of those achieved by the first step. We can therefore state that the application of centralised systems that allow for the application of different plans, brings an improvement, in all aspects, of over 11% and that the introduction of intelligent systems of a dynamic nature allows to increase this improvement of over 16%. In addition to a detailed study on the improvement in travelling time, which cannot be dealt with here, the reductions of energy consumption and pollutant emissions were analysed in detail• As a reference we will state that the percentage of heavy vehicles in the streets of the area was between 11% and 22%, which is fairly high for an urban area. The estimation of consumption and emissions was based on an existing study [10]. The various means were taken from average vehicles in the following positions [10]: (a) stopped position; (b) stable speed; (c) acceleration; and (d) deceleration• The measurements that were carried out have been correlated with the gauged traffic flow. The results of each kind of fuel and for each of the pollutants considered are shown in Table 2. It can be seen that consumption and pollutant emissions, considered separately, do not vary significantly from the overall average values shown in Table 1, i.e. the percentage improvements are similar for all kinds of pollutants considered.
The improvements also record another important result: that improvements of mobility are related to environmental improvements and reduction of energy consumption. This shows that the group of measures directed towards optimising the use of infrastructures through more efficient traffic
NO 2 EMISSIONS ','.. '.
.. -
".
fixed stages f i x e d schedules dynamic system
°,,,.,o,~
..... i.,o ~.~°°,
x ',
•
".•
• •
+ x
.
i..p°.30J~
kg " veh/hour CO~ EMISSIONS
f ~ e d stages f ~ e d schedules dynamic system ,00••,°L.
~°0M0]'
J=
',
!!i!i~!ii!
•.
",,
; !~!ii~iZ!! 1,,.0616 1,.,,~,,
'...
,,0.,J,.
,,°•.,,~
~,0.~lu ,,0.~,,,
•"
i,~.0°,~
~,~•t~,,
,~,.~,.
• •
,~o.,.,~ ~ , J . , ~ kg " veh/hour
Fig. 2. Relationship between air pollutant emissions and the traffic level.
50 control systems p r o d u c e s positive results in the three previous fields. These results, a n d o t h e r similar results o b t a i n e d in o t h e r cities, suggest that m a j o r i m p r o v e m e n t s can be achieved by a p p l y i n g the field o f t e l e c o m m u n i c a t i o n s to the t r a n s p o r t sector [11]. In o r d e r to c o m p l e t e the assessment o f the results obtained, an analysis was carried out o f the variation o f each o f the emissions with different levels of traffic, a c c o r d i n g to several routes established in the area o f study. The results o b t a i n ed, together with the d a t a from the survey and their extrapolation, after a regression analysis o f each variable with the traffic d e m a n d , for which values for r 2 o f over 0.7 were o b t a i n e d , are shown in Fig. 2.
4. Conclusions The experiments show the possibilities o f the direction a d v o c a t e d by the E U C o m m i s s i o n o f applying expert traffic c o n t r o l systems and thus diminishing the p r o b l e m s o f congestion a n d the associated negative e n v i r o n m e n t a l effects. T o g e t h e r with the measures o f traffic restriction in those areas where the m i n i m u m level is far exceeded, there are great possibilities in intelligent systems that a d a p t the d e m a n d to the 'environmental c a p a c i t y ' o f infrastructures. F r o m the results we can e x t r a p o l a t e that, within certain levels o f traffic, we can aim at optimising the objective o f m a x i m u m fluency in o r d e r to reduce congestion and its negative effects. T h a t is why it
,4. Monz6n de C6ceres / Sci. Total Environ. 146/147 (1994) 45-50
is essential to invest in the d e v e l o p m e n t o f efficient technical systems a n d in their i n t r o d u c t i o n into the cities, first at a pilot stage, to be able to a p p l y them on a general scale later.
5. References 1 Nijkamp P,, Urban traffic restrain measures: a road to success? In: Conference on Improving Traffic and Quality of Life in Metropolitan Areas. Council of Europe, Strasbourg, 1990. 2 Calder6n E., Trfifico Urbano y Medio Ambiente: un Ensayo de Planificaci6n Conjunta. Instituto de Estudios de Planificaci6n. Madrid, 1975. 3 PROGNOS, Development of Freight Transport in Europe. TTC, MTTC. Madrid, 1989. 4 Hills P. et al., Roads and Traffic in Urban Areas. Institution of Highways and Transportation. Department of Transport. HMSO. London, 1987. 5 Monz6n A., Impactos Ambientales de Carreteras. Carreteras, Vol. 47. Madrid, 1990. 6 Keller H.H., La Mod6ration de la Circulation en RFA. Actes du Congr6s 'Vivre et Circuler en Ville'. CETUR, Paris, 1990. 7 Mfiller P. et al., Bilanz zu Tempo 30. Grfine Reihe Nr. 11 des Fachgebiets Verkehrswesen. RFA, 1988. 8 Catling I., System convergence - - the potential for an integrated road transport environment. Transportation, 17 (1990) 285-299. 9 Ajuntament de Barcelona, Evaluaci6n del Sistema de Control de Trfifico del Area Sur. Servicio de Circulaci6n del Ayuntamiento de Barcelona, 1981. 10 MINER, Estudio y Diagn6stico de la Contaminacion Atmosf6rica en el Cintur6n Industrial de Barcelona. Madrid, 1981. 11 DRIVE, R & D in Advanced Road Transport Telematics in Europe, DRIVE'90. CED, DG Xlll, Brussels, 1990.