Chapter Three: Significant Findings

Policy

• The EU Environmental Noise Directive established an overall noise policy to encourage member states to reduce the exposure of populations to noise from transportation and industry sources.
• The EU directive required maps of noise exposure and action plans to reduce exposure to be developed and reviewed every 5 years of a 10-year plan for noise annoyance. Noise mapping must be delivered by July 2007 with identification of critical areas and action plans for these by July 2008. It supports out-of-the-box research on major highways.
• Noise annoyance surveys of the public are being used to determine annoyance in relation to noise levels measured on the new L den index.
• Several countries visited have established abatement guidelines and limit values.
• In several countries, noise characteristics are a critical performance indicator when selecting pavement strategies.

Design

• Recycling of PA was performed using a hot-in-place process in Italy to renew a porous layer.
• EAC surface has been used successfully in two countries to provide lower noise.
• Smaller aggregate size asphalt surface mixes using a dense or semidense gradation is the technique many EU countries use to obtain low-noise pavement surfaces. These mixes are used for low- to medium-speed traffic applications.
• PA systems with single-layer and double-layer systems are used or planned by several EU countries for significant noise reductions on high-speed facilities or facilities with significant truck traffic.
• Safety performance of low-noise surfaces has been maintained or enhanced compared to traditional pavement systems in all countries reviewed.
• Durability of low-noise pavement systems varies from 7 to 15 years, depending on the pavement system and the experience level of the owner agency.
• Low-noise pavement surfaces typically are assumed not to provide a structural contribution to the pavement, but some countries use a fractional structural contribution.

Noise Analysis

Measurement

1. CPX

   1. CPX methods vary among countries, and include the on-vehicle method.
   2. Research is still in progress on use.

2. Wayside measurements

   1. All countries use SPB, with some reporting results only for light vehicles.
   2. CPB is prevalent in Europe, but is not standardized.
   3. Some time-averaged measurements of traffic noise are used to gather SPB-like data.

3. Sound absorption

   1. Sound absorption is being measured in many countries. Standard ISO MLS methods are used. Moving methods seem especially useful but are not fully developed.
   2. Research is underway to develop a method for use with CPX to correlate to wayside measurements.

Modeling

• Adjust at source in model using SPB.
• Adjust at final level for simplified method.
• Model the relationship of pavement texture to noise.

Performance history

• Pavement noise-reduction benefits need to be presented with mention of the reference pavements.
• Only some of the countries have results for ageing pavement.
• Some countries presented spectral data.
• The noise-reduction benefits have been shown to be different for heavy trucks than for light vehicles. It has also been shown that these compose a substantial part of the traffic noise.
• Texture and porosity of pavements are important contributors to pavement noise.
• No good correlation exists between permeability and noise reduction.
• Wet pavement
• Quiet pavements allowing drainage help maintain or maximize the noise-reduction benefit during wet conditions.
• Retained moisture typically degrades performance for a day after rain.

Construction

• It is essential that the underlying structure be sound before any of the quiet pavement systems are applied. Most EU pavements have been constructed to what in the United States is termed “perpetual.” This has allowed EU countries to apply thin treatments or mill and replace without regard to structural constraints.
• Major differences exist in contract administration in Europe. Countries are moving from low bid to “low and best” bid. There are more design-build-maintain contracts, and even a few that include finance.
• There is a gradual move to performance-based specifications. If the contractor is required to warranty the pavement for several years, it must be responsible for design and inspection.
• No real field tests exist for acceptance on noise, with the exception of a permeability test in Italy. Performance is based on experimental sections and past experience, but is not tested on the project for compliance.
• A warranty generally is associated with all work, but in most cases it does not include noise.
• No special equipment or training is required for construction of the quiet pavement systems.

Maintenance

• Several countries visited indicated that porous surfaces have a tendency to clog. This appeared more prevalent on low-speed facilities.
• In winter conditions, porous surfaces do require a higher application rate of deicing chemicals (25 to 50 percent) to remove snow and ice.
• No consensus existed among the countries studied on whether pavement cleaning was beneficial and cost effective.
• EAC surfaces in the Netherlands (large stone and small stone), Belgium (large stone, optimized, Austrian two-layer system), and the United Kingdom appeared to provide a durable, noise-reducing surface.
• Considerable research is underway in Europe to provide additional information on measurement of texture for acceptance, durability of texture, skid resistance initially and over time, initial noise measurements, and acoustical durability for the porous surfaces.

Potential Implementation Issues

• Focus on noise characteristics when selecting pavements to support research of low-noise technologies.
• Investigate adding noise ratings to tires.
• Work with industry to develop and adopt noise standards.
• Increase the use of 9.5-mm SMA surface to provide additional noise reduction compared to traditional 12.5-mm or 19-mm dense-graded hot mix asphalt (HMA). SMA type surfaces used in Europe should be investigated for comparison to performance and maintenance issues on SMAs in the United States.
• Investigate the following pavement technology for application in the United States:
• EAC for portland cement concrete (PCC) surfaces
• Thin asphalt layers (4.75 mm and 6 mm), dense, semidense, and open asphalt surfaces for application on low-speed facilities
• TLPA systems for high-speed facilities or roadways with high truck traffic
• Diamond-grinding techniques to obtain low-noise surfaces on PCC pavements
• Investigate the structural contribution of low-noise surfaces for use in pavement design.
• Investigate variable density materials (expanded clay, slag, etc.) in asphalt concrete mixes.
• Investigate and monitor developments of the following pavement technologies for future implementation:
• Helmholtz resonator
• PERS
• Establish standards for noise measurement using sound pressure or intensity (on-vehicle method would be useful for portability).
• Standardize a CPB method in the United States.
• Standardize a time-averaging method, for situations in which SPB and CPX cannot be applied.
• Use sound absorption in combination with close proximity to correlate to wayside.
• Consider using sound absorption measurements for ground type implementation in the prediction model.
• Instead of SPB, use CPX to adjust source levels on a spectral basis, in combination with absorption measurements (this model implementation methodology needs to be established).
• Investigate and determine the appropriate spectral data to show whether narrow- band analysis is necessary.
• Research measurements related to heavy truck tire noise.
• In areas where wet weather is prevalent, construct pavements with good drainage to help maintain or maximize the noise-reduction benefit.
• Consider updating the existing noise policy to account for quiet pavements in noise modeling.