Copyright © 2000/08, C.J.Summers
THIS IS A GUIDE TO SOME ASPECTS OF ROAD NOISE
Personal
NoteMay I just take a moment of time to advise caution in this rush to make road surfaces "quiet".
It would not be wise to lose sight of the other qualities which are very necessary in a road surface, properties such as safety (skid resistance), whole life costing (durability) and problems with winter maintenance (increased salting and environmental pollution).
I am, of course, aware of the real intrusion road noise makes into the lives of some residents who live close to busy highways, but I am also aware of the potential of playing the "road noise card" in the marketing of many of the "new" proprietary bituminous materials.
I hope you will study carefully the information that is available on the subject of tyre generated noise before you come to a decision on the surfacing material you specify, and even if a "quiet surfacing" will be able to provide any benefit for a particular site, both in the short and long term.
And, do not forget the many low noise generating, bituminous mixtures for surface courses ( including 10mm. and 20mm. porous asphalt ) that are available as generic bituminous mixtures and which were specified in BS 4987 and BS 594, and will still be able to be specified from the various parts of BS EN 13108 : 2006:Bituminous mixtures. Material specifications
Old "reliables" such as 10mm. and 14mm. close graded surface course have have also been towards the bottom end of a range of bituminous mixtures accurately tested by TRITON for tyre generated noise.
And, you must not assume that all surface dressing causes increased tyre noise to be generated, as it will largely depend upon the type of dressing and size of chipping. Again there has been work conducted using TRITON, in comparative road surface trials that shows that dressings using 6mm. chippings cause low levels of tyre generated noise
May I draw your attention to the report,
TRL - Published Project Report PPR23 - Comparison of tyre road noise for a range of surfaces on the A47, A447 and B582 in Leicestershire
I am aware that there are a number of unpublished reports where TRITON was used to test for comparative levels of tyre generated noise on a number of surfaces, many of them "Thin Surfacings".
Details of some of these unpublished reports can be found on the Highways Agency website.
Speed of vehicles is found to be the most common factor in busy areas subject to high levels of tyre generated road noise. Therefore it is most necessary to look at the "speed of traffic" factor when considering tyre/road noise generation, you could spend a great deal of money on resurfacing and the locality affected by the tyre/road noise may not perceive any benefit.
Alternatively, if possible, you could reduce the speed of traffic in urban situations and gain a considerable benefit at little cost.
An interesting observation (and it is only an observation but voiced by many local residents) was made recently during a major motorway resurfacing contract.
The speed on the motorway during resurfacing was reduced to 50mph., however during the resurfacing period the volumes of traffic were the same as "normal".
During the time that the maximum speed was reduced the local residents thought that the resurfacing with a "quiet" surface had been completed and were very appreciative of this new surface.
However when the work was actually finished, and the speed restriction was removed, noise levels, whether tyre generated, engine generated, or "turbulence" generated, appeared to residents to return to the original levels.
I repeat that this is an "observation", and I am not aware of any noise level measurements taken during the work period. But anybody who has had anything to do with testing levels of tyre generated road noise knows that reducing speed of vehicles will considerably reduce the amount of noise produce from tyres.
A great deal of work is still ongoing on the subject of low noise generating road surfacing materials, and one avenue that appears to be showing potential is the use of smaller aggregate sizes, and this includes their use in surface dressings.
Finally, there is no such thing as a "quiet" road surfacing, some may generate less noise than others, and some may, especially in their early life, absorb a degree of generated noise, but they will not be "quiet" unless you do not run any traffic on them.
And, finally, finally, I am aware that there is a great deal of productive work being undertaken by tyre manufacturers to produce tyres that create less road generated noise. I believe that there may even be proposed European legislation relating to the amount of noise particular tyres will be allowed to produce in a standard test.
This is an area of the subject outside my personal knowledge, so I will not continue on this topic, but I am told that items relating to this area of total road noise reduction can be found on the internet if you do a little "searching" with appropriate key words.
TRL Report 237 - Commercial vehicle tyre adhesion
is just one of such document that contains information related to the tyre aspect of tyre generated road noise.
BELOW IS A BRIEF COLLECTION OF INDIVIDUAL ITEMS RELATED TO ROAD NOISE GENERATION, AND REFERENCE TO A NUMBER OF REPORTS AND SPECIFICATIONS WHERE FURTHER INFORMATION ON THE SUBJECT CAN BE OBTAINED.
There are also links to a number websites where you will find useful information in relation to road noise, and the general subject of ambient levels of noise, at the bottom of this page.
WHAT IS NOISE, AND HOW DO WE QUANTIFY IT
I was getting a little confused with the ‘‘noise’’ figures quoted relating to the differing types of road surfacing materials, figures quoted in differing technical documents, publicity handouts and articles in magazines were not correlating.
So I consulted a colleague, not a "noise" expert as such but he knows an awful lot about Hi-Fi equipment, and from articles in magazines he loaned me, I determined the following.
Because of the logarithmic basis of the scale that measures noise, a doubling in loudness corresponds to a 10 fold increase in the sound energy which equates to an increase in the sound pressure level of 10db(A), e.g. an 80db(A) noise is twice as loud as a 70db(A) noise.
A doubling of the energy level, for example doubling the traffic volume at any point in time, increases the noise level by 3db(A).
So when I read, in some glossy brochure, that the "noise" has been halved by using a particular surfacing material, which statement do I refer to, because there are a lot of db(A)'s difference.
Also, for the recorded road noise levels
of the various road surfaces to mean anything all
measurement should be performed by the same test method
with similar traffic traveling at similar speeds.This careful comparison of differing surface materials is just not happening at the moment , so please take care when choosing a surfacing material for a "noise sensitive" site.
When we start to see more work published from the TRL that has been produced by TRITON, a sophisticated tyre noise survey vehicle perhaps things will be a little less vague.
To date I am only aware of one published report, this is,
TRL - Published Project Report PPR23 - Comparison of tyre road noise for a range of surfaces on the A47, A447 and B582 in Leicestershire
This is a thoroughly informative report providing detailed information on TRITON itself, and accurately obtained comparative tyre generated noise readings for a number of different types of road surface.
It can be obtained from the Transport Research Laboratory (TRL), and only costs about £20:00.
BS EN 1793 : Parts 1 to 3 : Acoustic performance of noise barriers
BS EN 14388 : 2005 : Road traffic noise reducing devices - Specifications
This document specifies the performance requirements and methods of evaluation for road traffic noise reducing devices.
This document covers acoustic and long term performance, but not aspects such as resistance to vandalism or requirements of visual appearance.
This document covers products used for road traffic noise reduction made from any materials.
This document does not cover road surfaces or the airborne sound insulation of houses.
This document does not cover material specific characteristics necessary to meet the performance requirements of the standard, if existing, material specific standards should also apply in accordance with the specifications.
BS EN 14389-2 : 2004 : Road traffic noise reducing devices - Procedures for assessing long term performance -
Part 2 : Non-acoustical characteristics
This document specifies assumed working life requirements and is also intended to assist suppliers in its prediction.
BS EN 1794-2 : 2003 : Road traffic noise reducing devices - Non-acoustic performance -
Part 2 : General safety and environmental requirements
DTP DESIGN MANUAL FOR ROAD AND BRIDGES - VOLUME 7
This volume has been updated and organised into 4 sections containing 10 new combined Standards and Advice Notes and 2 existing Technical Memoranda.
It gives information/advice for design, construction, assessment & maintenance of road pavements.
The title of Vol. 7 is PAVEMENT DESIGN AND MAINTENANCE, it includes:-
HD 36/99 : Surfacing for New and Maintenance Construction, which includes a section on tyre/road surface noise.
HD 37/97 : Bituminous Surfacing Materials and Techniques, this design manual includes section on surfacing materials that will provide a road surface on which a tyre will generate less noise.
Such materials as Porous Asphalt, Stone Mastic Asphalt, and proprietary "Thin Surfacings".
DTP DESIGN MANUAL HD 36/99 - PSV - SKID RESISTANCE - PERMITTED BITUMINOUS SURFACING MATERIALS - NOISE
HD 36/99 defines specification requirements for POLISHED STONE VALUES and AGGREGATE ABRASION VALUES for new bituminous surfacings, including resurfacing and surface dressing, for trunk roads.
This standard supercedes/updates parts of HD 28/94 which superseded HD 21/92 which superseded HD 16/76, although much reference to skid resistance remains in HD 28/94.
It includes tables of permitted surfacing materials with reference to other design manuals where further information can be found on these materials.
HD 36/99 also has a section on tyre noise.
This section of Volume 7 of the DESIGN MANUAL gives good information on the nature of SKID RESISTANCE, PSV's, AAV's, skid resistance of roads and means of assessing skid resistance, and the related skid resistance surveys/investigation levels.
FRICTION COURSE - PERVIOUS MACADAM
FRICTION COURSE is/was the term ( the name is little used now ) for a bituminous material that has a high voids content to allow drainage of surface water through the WEARING COURSE onto an impermeable BASECOURSE and by a suitable cross fall to a drain.
The material was devised to reduce spray being thrown up by vehicles and aquaplaning.
It has also been found to reduce road noise.
This type of material is now more commonly known as PERVIOUS MACADAM or POROUS ASPHALT.
Associated problems with this material have been:-
1) A reduced design life compared to conventional HRA wearing course.
2) The interstices through which the water drains become blocked with road detritous.
3) Some surfaces have had frost damage.
POROUS ASPHALT WEARING COURSE
The name POROUS ASPHALT is technically misleading this material is not an ASPHALT in its make up and characteristics as UK road engineers traditionally understand by the term ASPHALT.
POROUS ASPHALT is a STIFF open graded macadam.
It was specified in :-
BS 4987: Coated macadams for roads and other paved areas
Clauses :-
2.8.1 MACADAM, 10MM. SIZE POROUS ASPHALT WEARING COURSE
2.8.2 MACADAM, 20MM. SIZE POROUS ASPHALT WEARING COURSE
In the BS 4987:1993 edition the mixture description PERVIOUS WEARING COURSE was changed to POROUS ASPHALT WEARING COURSE, this is a change from the descriptions found in BS 4987:1985
These bituminous mixtures still remained in the 2005 edition of BS 4987.
POROUS ASPHALT will reduce spray during wet weather, it will also reduce road noise.
This has to be balanced against increased costs and a considerably reduced life compared to a conventional 30%/14mm. H.R.A. asphalt wearing with a PRECOAT layer.
BS 4987, and BS 594 have been superseded by the family of specifications for bituminous mixtures contained in,
BS EN 13108 : 2006:Bituminous mixtures. Material specifications
REPORT VTI SARTRYCK 323 : 1999 : LOW NOISE ROAD SURFACES - SWEDISH NATIONAL ROAD AND TRANSPORT RESEARCH INSTITUTE
This is a "state of the art" review investigating tyre generated road noise in relation to varying road surfaces and tyres.
REPORT VTI SARTRYCK 325 : 1999 : NOISE : THE CHALLENGE - SWEDISH NATIONAL ROAD AND TRANSPORT RESEARCH INSTITUTE - TYRES - ROAD SURFACES - SKID RESISTANCE
This is a study on a number of types of tyres investigating the noise, friction and rolling resistance of each tyre type with relation to differing road surfaces.
THE ENVIRONMENTAL NOISE BARRIER ASSOCIATION - ENBA
TRITON - TRL NOISE MEASURING VEHICLE
TRITON is claimed to be a unique tyre/road noise investigation vehicle.
TRL assisted in the development of the noise test for HAPAS and refined a Statistical Pass-by method with TRITON so that highway authorities can more accurately assess the noise producing properties of various surfacings.
Unfortunately much of the work undertaken by TRL using TRITON has not been published.
TRL REPORT 237 - COMMERCIAL VEHICLE TYRE ADHESION - TYRE NOISE
Includes information on tyre noise.
TRL Report TRL536 - Resurfacing a motorway with porous asphalt : Effects on rural noise exposure and community response
TRL Report TRL545 - Development of a novel traffic calming surface "Rippleprint"
This report details the stages involved in developing traffic calming surfaces with particular reference to surface that has a sinusoidal wave pattern created on the surface of the road the design of the wave is such that noticeable vibration is cause within the vehicle cabin without cause excessive noise to the close environment
TRL Report TRL576 - Quieter concrete roads : construction, texture, skid resistance and noise
Exposed aggregate concrete road surfaces compared with hot rolled asphalt, stone mastic asphalt and thin surfacings.
TRL - Published Project Report PPR23 - Comparison of tyre road noise for a range of surfaces on the A47, A447 and B582 in Leicestershire
This is a thoroughly informative report providing detailed information on TRITON itself, and accurately obtained comparative tyre generated noise readings for a number of different types of road surface.