This report presents a series of methods implemented in Denmark and other European countries for the assessment and control of the impacts of highway noise on the neighboring public. It introduces Danish guidelines for the assessment of noise impact. Also described are examples of noise abatement planning for three different cases: planning of new highways, planning of highway widening projects, and noise abatement on existing highways. Experience shows that there is no single approach that can remove all noise problems along highways. It will be necessary for more effective noise abatement to take different approaches together, including noise-reducing pavements, noise barriers, facade insulation, and proper land use strategies. Harmonized public-private partnership is also critical for successful implementation of public policy and regulations related to noise abatement.

Noise barriers are widely used as an effective means to abate highway traffic noise. With public interest in eco-friendly and aesthetic designs for noise barriers growing, highway agencies are exerting greater efforts to provide the public with “green” noise barriers that are functionally sound as well as adaptive to the surrounding environment. This report presents a summary of green noise barrier design practices experienced by the Danish Road Institute (DRI-DK) and other European countries for the last two decades. Some example noise barrier designs are described with recommendations for more effective and innovative ones. The report contains a recommendation to use varied approaches in green noise barrier designs that are adapted to urban and rural settings.

The work described in this report is adjunct to a five-year study of tire/pavement noise undertaken by the University of California Pavement Research Center for the California Department of Transportation under the Partnered Pavement Research Center program (PPRC). This part of the study was performed in cooperation with the Danish Road Institute/Road Directorate, and it examined the influence of air temperature on tire/pavement noise measurements performed on two types of tires (Aquatred and Standard Reference Test Tire [SRTT]) on different asphalt pavement surfaces using the On-board Sound Intensity (OBSI) method. Field noise measurement testing was carried out in two series: one in the Southern California desert on State Route 138 using the SRTT, and the other with data collected on a statewide selection of pavements tested with the Goodyear Aquatred tire in an earlier part of the PPRC noise study. The field measurements yielded data for deriving air temperature coefficients for the two types of tires, and a comparison of them is made. A worldwide survey of the available literature accompanies the field work and analysis, and a summary of it is used to compare the air temperature coefficients of the SRTT with a combination of tire types used in European testing. In addition, findings in the literature serve as the basis for a series of predicted temperature coefficients for passenger cars on various cement concrete and asphalt pavements. Finally, the report presents ten general conclusions drawn regarding the relationship between air temperature correction and tire/road noise on asphalt and concrete pavements.

The level of noise generated by tire/pavement interaction of a pavement section changes over time. While the general consensus is that the noise level tends to increase as the pavement ages, more scientific investigation is necessary to better understand the process of acoustic aging of pavements. For more than a decade, independent studies by Caltrans and the Danish Road Institute (DRI-DK) have included monitoring of tire/pavement noise levels on selected pavements. Using data sets collected as part of those studies, a comprehensive analysis was conducted in this study to characterize the acoustic aging properties of different types of asphalt pavements. Pavement types considered in the analysis include dense-graded asphalt concrete (DGAC), open-graded asphalt concrete (OGAC), thin open-graded asphalt layer, and porous asphalt concrete (PAC). This report presents the results of the data analysis in terms of the relative changes of tire/pavement noise over time for the respective pavements. It also describes the development of an acoustic aging model for asphalt pavements. The model predicts the increase in noise level as a function of pavement age, traffic volume, and pavement type, primarily for highways with speeds over 50 mph. Further study is recommended to improve the prediction model and to integrate the noise model in a Pavement Management System.