Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/412488
RoadScience 8 November 2014 Better Roads need to be addressed when consider- ing quiet pavement technology." Based on the results of the evalua- tion, a methodology that uses on- board sound intensity [OBSI] data to quantify the noise levels of existing and future pavement projects was de- veloped, including their performance over time. The methodology also considers modification of the Federal Highway Administration's Traffic Noise Model (TNM), used to predict future highway noise resulting from capac- ity improvements, and life cycle cost analysis to evaluate the initial cost of abatement and cost of maintaining that performance over the life of the project. Download this important new document by searching for "NCHRP 738" on the web or by going to http://onlinepubs. trb.org/onlinepubs/nchrp/nchrp_rpt_738.pdf. To build or not build? Today, noise barriers are constructed for what are termed Type I highway projects, defined as either construction of a highway on new location, or the physical alteration of an existing highway which significantly changes either the horizontal or vertical alignment, or increases the number of through-traffic lanes. As agencies don't want to build noise walls that don't serve enough residents, parks or businesses to make them worth building, the walls must meet feasibility criteria. An environmental review is required for Type I projects, and, using the TNM, if a significant future reduction in sound can be attained at a number of observation points ("receiv- ers") at or near buildings, a noise barrier is determined to be reasonable cost-wise, thus feasible, and eligible for federal funding. The cost-effectiveness is determined by assigning a value to the square footage required of the barrier, the total of which can't exceed a certain value per benefited receiver. If there aren't enough benefited receivers to justify the wall, it doesn't get funded. In Maine, the cost per benefited receiver can't exceed $31,000 or the barrier is deemed not feasible. Type II or "retrofit" projects are noise abatement projects along existing highways. The implementation of a Type II program is not required by federal regulations, but might be eligible for federal-aid funding if the state agency fol- lows guidelines. Otherwise these must be paid entirely by the agency or by private fundraising, for example, from nearby residents. For more info go to fhwa.dot.gov/environment/noise. New FHWA guidance on noise barriers was provided late last year and can be downloaded at fhwa.dot.gov/environment/noise/ noise_barriers/acceptance_criteria/analysis/analysis.pdf. Evaluating lower-cost barriers With costs ranging from $2 million to nearly twice that, agencies are looking for lower-cost alternatives to sound barriers, especially for the Type II projects which don't get federal funding. A new, lower-cost form of noise barrier is the line-of-sight (LOS) barrier, which can make limited sound suppression more widely available in urban and sub- urban neighborhoods. The line-of-sight noise wall is just tall enough to break the horizontal line of sight between the highway (noise source) and the home (noise receiver), report Shuo Li, Ph.D., P.E., and Samy Noureldin, Ph.D., P.E., Indiana DOT, and Bowen Guan, Purdue University, and Yingzi (Eliza) Du, Ph.D., Indiana University-Purdue University, in their 2014 Transportation Research Board paper, Residents' Perceptions and Attitudes toward to Line of Sight Wall and Conventional Concrete Noise Wall for Traffic Noise Abatement. "Since the eye level height at a standing position is 67 inches for the average U.S. adult, the height of [a] LOS wall may be around 6 feet," they write. "While the LOS wall does not fit into the current noise wall policy and could not use federal funds for construction, it may achieve a 5 dBA noise level reduction and provide a measure to improve Photo courtesy of Tom Kuennen In Florida, precast noise barriers suppress sound in adjacent residential neighborhood