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H. Bendtsen, J. Haberl, U. Sandberg, G. Watts, J. Litzka, E. Pucher (Hrg.):
"Traffic management and noise reducing pavements - recommendations on additional noise reducing measures";
Danish Road Institute, Report 137, 2004, ISBN: 87-91177-55-3; 106 S.

This report is produced as Deliverable 12 - "Recommendations on Additional Noise Reducing Measures" - of the EU research project SILVIA. The report is the outcome of the work carried out by a working group in task 5.3 of working package 5 of the SILVIA project. The goal for task 5.3 is to investigate traffic management measures in order to highlight their capacity for noise control and to evaluate the possibilities and effects of combining traffic management measures with the use of noise reducing pavements especially in urban areas. The main goal of this document is to describe recommendations for road administrators with respect to additional noise reducing measures.
Traffic management measures such as environmentally adapted "through" roads, 30 km/h zones, road humps, roundabouts, restrictions on traffic in special periods, speed control etc are used on many urban roads in Europe. These measures are usually applied to improve traffic safety, typically by reducing the speed, and to "calm" residential areas from the environmental impact caused by the traffic in order to make the areas more pleasant to live in for the residents and more agreeable to shop and walk in for shoppers and other people. The term "traffic management" can be described as an application of different strategies and measures to change the flow of traffic on roads either to reduce the speed of vehicles passing by and/or to reduce the traffic volume itself. This will all have an effect on the environmental noise caused by vehicles.
The first part of the report is focused on analysing the relations between speed and noise. The effects of uneven driving pattern with accelerations and braking are included. This is analysed on the background of prediction models like the Nordic Method and the Harmonoise method developed in an EU project. The second part of the report is a comprehensive European literature survey to find and compile existing relevant knowledge on relations between traffic management and noise. On this background the final results and recommendations are developed.
Modelling noise
The use of new emission data for the Nordic Noise Prediction method shows that for urban driving at speeds in the range of 30 to 60 km/h a speed reduction of 10 km/h for light vehicles reduces the noise by up to 2 to 4 dB depending on the starting point. For heavy vehicles the reduction potential is 2 to 3 dB. For speed reductions of 10 km/h in the speed range from 110 to 60 km/h the noise reduction will be about 1 to 2 dB for roads with 10 % heavy vehicles
In some cases traffic management is used to reduce the amount of traffic on a road and/or to reduce the percentage of heavy vehicles. A 10 % reduction of traffic only leads to a 0.5 dB noise decrease, whereas a 50 % reduction decreases noise by 3 dB. On a road with 10 % heavy vehicles the noise will be reduced by 1 to 2 dB if all the heavy vehicles are removed.
The driving pattern also has an influence on noise levels, although uneven driving patterns usually do not dominate under normal driving conditions. At moderate accelerations the noise can increase by up to 2 dB (in comparison to constant driving speed) where such accelerations occur (which may be on rather limited locations) depending on the mix of vehicles. This is a little less than the reduction achieved by a speed reduction of 10 km/h. It is therefore important to design speed reduction measures in such a way as to avoid accelerations and decelerations as much as possible and to ensure that the accelerations do not occur at or near the position of dwellings or other noise-sensitive areas.
Traffic management examples
In the table underneath the results of the literature survey are summarised. The effect on noise is based on estimates of up to approximately 10% of heavy vehicles. The effect on noise of the different traffic management measures depend very much of the precise design and implementation of the measures as well as on how they are accepted by the drivers. Generally it can be concluded that reductions in average noise levels (LAeq) of up to 4 dB can normally be achieved but in special situations even higher reductions may be reached. But some speed reducing measures might increase noise like rumble areas and paving stones. Vertical deflections such as humps and cushions can reduce the average levels due to significant speed reductions but the maximum levels can increase due to body rattle noise produced as some vehicles (especially empty container lorries) negotiate the deflection. The actual reduction in the average level will depend critically on the percentage of heavy vehicles in the traffic stream.

Traffic management measure
Potential noise reduction (LAeq)
Traffic calming / Environmentally adapted through roads Up to 4 dB
30 km/h zone Up to 2 dB
Roundabouts Up to 4 dB
Round-top/circle-top road humps Up to 2 dB
Flat-top humps Up to 6 dB increase
Narrow speed cushions Up to 1 dB increase
Night time restrictions on heavy vehicles Up to 7 dB at night time
Speed limits combined with signs about noise disturbance 1 - 4 dB
Rumble strips of thermoplastic Up to 4 dB noise increase
Rumble areas of paving stones Up to 3 dB noise increase
Rumble wave devices 0 dB

The following general conclusions and recommendations in relation to noise can be drawn:
1. Speed reductions reduce noise.
2. However the noise from some heavy vehicles can in some cases increase due to increased gear shifting and body rattle noises.
3. In order to achieve a reduced speed it is normally not enough just to install speed limit signs. It is also necessary to redesign and rebuild the road so that the physical layout matches the intended speed.
4. Visual speed reducers are often effective in reducing noise.
5. It is important to achieve as smooth a driving pattern as possible.
6. It is important to minimise uneven driving patterns. This can be done by having appropriate distances between speed reducers.
7. It is important to achieve driving patterns where the vehicles are not brought to a complete stop as this generates more noise from decelerations and accelerations.
8. Speed reducers which displace the vehicles to the left or to the right are often effective in reducing noise especially in the case of heavy vehicles.
9. Speed reducers which change the vertical height of parts of a road (like some types of road humps) can in some cases be problematic in relation to noise, especially for heavy vehicles, where body rattle noises can produce large peaks in noise levels as these vehicles cross the vertical deflections.
10. The use of rumble areas, for example with paving stones, increases noise.
11. There are reports of cases with increased perceived annoyance even though the average noise level has decreased.
12. There are reports on increases in the perceived noise annoyance because of impulse-like noise, rattling in the bodywork or cargo of heavy vehicles, as well as short-time changes in the sound level and frequency caused by gear shifting or changing in engine revolutions due to acceleration or braking of a vehicle.
13. Speed reducers, which change the vertical height of parts of a road, may produce perceptible levels of vibrations in nearby houses. This depends on the type of ground condition and distance from the vertical deflection to the nearest house foundations. Serious annoyance has been reported especially where houses are close to road humps built on soft ground such as peat soils and alluvium deposits.
14. Speed reductions generally have a good effect on traffic safety.
In a Danish report it has been suggested that 5 dB should be added as a "penalty" to the actual noise level if impulsive noise or similar is occurring (for example where rumble areas/strips or paving stones are used) to compensate for the increased perceived annoyance. It must generally be concluded that more research is needed to investigate and quantify the effect of impulsive noise from road traffic, especially in relation to certain types of speed reducers. A general recommendation could be, on the background of the existing knowledge, to place speed reducers which change the vertical height of parts of a road and/or include rumble areas at a distance as long as possible from houses where people are living.
Traffic management and noise reducing pavements
It is obvious that it can be a good idea to combine traffic management measures and the use of noise reducing pavements in noise abatement schemes. Generally there does not seem to be any technical arguments for not combining these measures of noise abatement. However, it must be noted that porous pavements can be damaged on bends, junctions and roundabouts sites where forces at the tyre/road interface are relatively high. This must be taken into consideration when applying porous pavements on roads specially constructed to reduce speed. Speed reducers which displace the vehicles to the left or right may be problematic for the durability of porous pavements, because this will make the vehicles drive in curves for short distances. But other types of noise reducing pavements can be used in such cases.
In other parts of the SILVIA project the noise reducing effect of different pavement types are documented. On urban roads with speeds in the range from 40 to 60 km/h noise reductions of 1 to 4 dB can be achieved by using for example noise reducing thin layers or porous pavements. At higher speeds the noise reducing potential for these pavements may be up to 6 dB or even more. This noise reduction is of the same magnitude as or higher than the reduction which can normally be achieved by traffic management measures.
Noise reducing pavements and traffic management measures may influence the frequency distribution of road traffic noise in different ways, and this can have an influence on the total noise reduction. For simplification it can anyway be recommended to add (on a dB basis) the effect of the two types of noise reduction. It is therefore generally on urban roads possible to obtain noise reductions of 3 to 8 dB by combining the use of noise reducing pavements and traffic management measures. On highways with high speeds the potential for noise reduction may be up to 10 dB or even more.
Generally noise reducing pavements have a better reduction effect on noise from light vehicles than on noise from heavy vehicles. This means that if a traffic management measure such as an environmentally adopted street or a 30 km/h zone has an effect on reducing the percentage of heavy vehicles the beneficial effects of the noise reducing pavements will be increased.
Research needs
The literature has shown that noise reductions due to the introduction of traffic management schemes can result in both positive and negative responses from the inhabitants. In some cases social surveys have shown a significantly reduced perceived annoyance and in other cases the perceived annoyance has increased even though the measured average noise levels have decreased. As the main goal of noise abatement is to improve the life quality for people there is a need for further research in this field. Research themes could be:
. The effect of different designs of road humps and cushions on the perceived annoyance.
. The effect of different types of rumble areas and strips on the perceived annoyance.
. Development and optimization of traffic management schemes in order to reduce the perceived annoyance as much as possible.
. Investigation and quantification of the effect on the perceived annoyance of impulsive noise from road traffic, especially in relation to certain types of speed reducers like humps and rumble areas.
. The effect on the perceived annoyance when combining traffic management and noise reducing pavements in order to reduce noise.
Very few references have been retrieved where the use of advanced information technology and automatic traffic steering and management has been developed and investigated. Therefore there is also a need to focus on this field in research and development projects. In this research it will also be relevant to focus on projects where noise reducing pavements are included. There is a need to develop methods to build vehicle sensors into the surface of porous pavements without damaging the capacity of the porous pavement to lead rain water to the roadside.
There is also a need to further develop and test speed reducers such as rumblewave devices which can generate noise inside the vehicles but at the same time do not have any negative effect on the noise along the roads.