- Email: [email protected]
Aspects of construction: The new urban roads
J. Sound Vib. (1971) 15 (l), 35-39
ASPECTS OF CONSTRUCTION:
THE NEW URBAN ROADS-f
D. DENNINGTON Greater London Council, County Hall, London, S.E.1, England (Received 12 March 1970) This country is beginning to enter a phase of major road construction within urban areas. It has been slower to build such roads than other countries where, it seems, the additional source of noise they bring has gone unheeded. This paper considers what alternative measures may reduce the noise climate adjacent to these roads, on the presumption that vehicle noise is not reduced at source. There is, as yet, no positive recom-
mendation concerning the form a screen should take within the limits of the road, but their effective use may be possible only along moderate stretches of road. If noise is to be abated it will cost the public money either in a direct or indirect form.
1. INTRODUCTION
This country is beginning to enter a phase of major road construction within urban areas. It has been slower to build such roads than other countries where, it seems, the additional source of concentrated noise they bring has gone unheeded. Nevertheless, prior attention is being given to the matter here. It is a premise that limited access roads of motorway standards, if not tolled, and gradeseparated junctions will attract a high proportion of their capacity in all forms of vehicles. Noise from free-flowing traffic is made up of engine noise and wheel noise. At the average 40 m.p.h. speeds to be anticipated on the new roads, wheel noise will not be dominant and it is unlikely to be abated at source whilst increasing attention is paid to the necessity of good road-holding properties. It is the engine noise that predominates and the heavy commercial vehicle is the prime contributor. If the noise of heavy vehicles could be reduced at source, little or, no additional measures would be required to protect residents, near to the roads, from what is at present considered an undesirable noise situation. This paper considers what alternative measures may reduce the noise climate adjacent to these roads, on the presumption that vehicle noise is not reduced at source.
2. FORMS OF ROAD CONSTRUCTION The basic forms of construction associated with new urban roads are listed below. (1) Elevated roads : (a) flyovers, (b) continuous roads on structure or embankment. (2) Ground level roads. (3) Depressed roads: (a) underpasses, (b) continuous roads in cutting with vertical or sloping sides. (4) Tunnels. t Presentedat the symposium on “Road and environmental planning and the reduction of noise” held on 24 to 28 March 1969 at the University of Southampton, Southampton, England. 35
36
D. DENNINGTON
In general, (la) and (3a) refer to grade-separated junctions and the remaining categories to limited access roads or urban motorways. Tunnels do not contribute to the noise problem. In most minds the urban motorway is associated with elevated roads; there is good reason for this in London where this form has been adopted for the M4 extension and the elevated Western Avenue is under construction (Plate 1). Other motorways are, however, under construction or being planned in the capital and in terms of the total mileage the percentage forms of constuction are as follows: elevated, 18 %; ground level 61%; depressed 18 %; tunnel 3 %. The elevated and depressed elements may themselves be further split as follows. Elevated : on structure 88 %, on embankment 12 ‘A. Depressed: between vertical walls 83 ‘A, between side slopes 17 %. The grade-separated junctions, or interchanges, associated with the connection of these motorways to each other and existing routes will add further effective road lengths equal to 60 % of the motorways themselves. These figures represent a total road pattern requiring 20 years to achieve, but they serve as a proportional guide to the forms of roads to be expected. The preponderance of ground level roads is to be noted. The basic standard for motorways, sought where possible, is dual three-lane carriageways with hard shoulders, about 100 ft wide overall. 3. GRADE-SEPARATED
JUNCTIONS
Improvements of existing junctions by grade separation take the form of flyovers or underpasses, or both; Plates 2 and 3 illustrate good examples of such methods. Both photographs were taken in mid-afternoon, and the number of heavy vehicles present in Plate 2 is significant in respect of noise; even in Plate 3 one-quarter of the vehicles shown are heavy ones. The flyovers now being constructed usually have some solid parapet about 3 ft high to serve multi-functions, to protect those below from splash, loose wheel caps and, to some extent, noise. The overall improvement of junctions incorporating flyovers usually requires a generous land take and often the increase of noise due to increased traffic flow is mitigated by the extra distance that separates it from dwellings; Plate 2, however, shows an exception to this in one quarter. Traffic forced to start and stop at a junction before its improvement might well be an equal noise nuisance, in some minds, to the noise caused by additional vehicles flowing more smoothly. A source of noise not usually considered is that due to the structural road joints necessary to accommodate the thermal movements of long continuous structures; badly designed or constructed, they may cause loose lorry loads to shift to the extreme irritation of those close by. Good design is the only remedy. Underpasses have a curious attraction to speed assisted by the initial downward gradient, about 1 in 20. Nevertheless, heavy vehicles have to change gear to emerge, thus increasing their noise. This factor is also present with the approach gradients to flyovers. In underpasses, the vehicle drivers themselves experience an increase of noise due to the reflection of sound from the walls, prior to its escape, to affect nearby dwellings. The widthto-depth proportions of a four-lane underpass are about 4 : 1, so that the direct escape angle of noise from a slow lane is low enough to directly affect nearby opposite dwellings. There may also be reflected noise. The most convenient and economical form of underpass wall construction is concrete, utilizing the “as struck” surface with a minimum of surface dressing. There is scope, however, for an applied secondary finish, which is sometimes required for other reasons, and this may be made sound-absorbent to reduce reflected noise. Such a finish is to be used on a current
Plate 1. Western Avenue extension.
(fucingp.
36)
Plate 2. Bow Bridge flyover.
Plate 4. Blackwall Tunnel-southern
approach.
ASPECTS OF CONSTRUCTION:
THE NEW URBAN ROADS-f
D. DENNINGTON Greater London Council, County Hall, London, S.E.1, England (Received 12 March 1970) This country is beginning to enter a phase of major road construction within urban areas. It has been slower to build such roads than other countries where, it seems, the additional source of noise they bring has gone unheeded. This paper considers what alternative measures may reduce the noise climate adjacent to these roads, on the presumption that vehicle noise is not reduced at source. There is, as yet, no positive recom-
mendation concerning the form a screen should take within the limits of the road, but their effective use may be possible only along moderate stretches of road. If noise is to be abated it will cost the public money either in a direct or indirect form.
1. INTRODUCTION
This country is beginning to enter a phase of major road construction within urban areas. It has been slower to build such roads than other countries where, it seems, the additional source of concentrated noise they bring has gone unheeded. Nevertheless, prior attention is being given to the matter here. It is a premise that limited access roads of motorway standards, if not tolled, and gradeseparated junctions will attract a high proportion of their capacity in all forms of vehicles. Noise from free-flowing traffic is made up of engine noise and wheel noise. At the average 40 m.p.h. speeds to be anticipated on the new roads, wheel noise will not be dominant and it is unlikely to be abated at source whilst increasing attention is paid to the necessity of good road-holding properties. It is the engine noise that predominates and the heavy commercial vehicle is the prime contributor. If the noise of heavy vehicles could be reduced at source, little or, no additional measures would be required to protect residents, near to the roads, from what is at present considered an undesirable noise situation. This paper considers what alternative measures may reduce the noise climate adjacent to these roads, on the presumption that vehicle noise is not reduced at source.
2. FORMS OF ROAD CONSTRUCTION The basic forms of construction associated with new urban roads are listed below. (1) Elevated roads : (a) flyovers, (b) continuous roads on structure or embankment. (2) Ground level roads. (3) Depressed roads: (a) underpasses, (b) continuous roads in cutting with vertical or sloping sides. (4) Tunnels. t Presentedat the symposium on “Road and environmental planning and the reduction of noise” held on 24 to 28 March 1969 at the University of Southampton, Southampton, England. 35
36
D. DENNINGTON
In general, (la) and (3a) refer to grade-separated junctions and the remaining categories to limited access roads or urban motorways. Tunnels do not contribute to the noise problem. In most minds the urban motorway is associated with elevated roads; there is good reason for this in London where this form has been adopted for the M4 extension and the elevated Western Avenue is under construction (Plate 1). Other motorways are, however, under construction or being planned in the capital and in terms of the total mileage the percentage forms of constuction are as follows: elevated, 18 %; ground level 61%; depressed 18 %; tunnel 3 %. The elevated and depressed elements may themselves be further split as follows. Elevated : on structure 88 %, on embankment 12 ‘A. Depressed: between vertical walls 83 ‘A, between side slopes 17 %. The grade-separated junctions, or interchanges, associated with the connection of these motorways to each other and existing routes will add further effective road lengths equal to 60 % of the motorways themselves. These figures represent a total road pattern requiring 20 years to achieve, but they serve as a proportional guide to the forms of roads to be expected. The preponderance of ground level roads is to be noted. The basic standard for motorways, sought where possible, is dual three-lane carriageways with hard shoulders, about 100 ft wide overall. 3. GRADE-SEPARATED
JUNCTIONS
Improvements of existing junctions by grade separation take the form of flyovers or underpasses, or both; Plates 2 and 3 illustrate good examples of such methods. Both photographs were taken in mid-afternoon, and the number of heavy vehicles present in Plate 2 is significant in respect of noise; even in Plate 3 one-quarter of the vehicles shown are heavy ones. The flyovers now being constructed usually have some solid parapet about 3 ft high to serve multi-functions, to protect those below from splash, loose wheel caps and, to some extent, noise. The overall improvement of junctions incorporating flyovers usually requires a generous land take and often the increase of noise due to increased traffic flow is mitigated by the extra distance that separates it from dwellings; Plate 2, however, shows an exception to this in one quarter. Traffic forced to start and stop at a junction before its improvement might well be an equal noise nuisance, in some minds, to the noise caused by additional vehicles flowing more smoothly. A source of noise not usually considered is that due to the structural road joints necessary to accommodate the thermal movements of long continuous structures; badly designed or constructed, they may cause loose lorry loads to shift to the extreme irritation of those close by. Good design is the only remedy. Underpasses have a curious attraction to speed assisted by the initial downward gradient, about 1 in 20. Nevertheless, heavy vehicles have to change gear to emerge, thus increasing their noise. This factor is also present with the approach gradients to flyovers. In underpasses, the vehicle drivers themselves experience an increase of noise due to the reflection of sound from the walls, prior to its escape, to affect nearby dwellings. The widthto-depth proportions of a four-lane underpass are about 4 : 1, so that the direct escape angle of noise from a slow lane is low enough to directly affect nearby opposite dwellings. There may also be reflected noise. The most convenient and economical form of underpass wall construction is concrete, utilizing the “as struck” surface with a minimum of surface dressing. There is scope, however, for an applied secondary finish, which is sometimes required for other reasons, and this may be made sound-absorbent to reduce reflected noise. Such a finish is to be used on a current
Plate 1. Western Avenue extension.
(fucingp.
36)
Plate 2. Bow Bridge flyover.
Plate 4. Blackwall Tunnel-southern
approach.