TRAFFIC NOISE EFFECTS OF ELEVATED, DEPRESSED, AND AT-GRADE LEVEL FREEWAYS IN TEXAS

To answer questions being raised by abutting residents and businesses about proposed elevated and/or depressed freeway improvements in the urban and suburban areas of Texas, a four-year study has been conducted to estimate the social, economic, and environmental effects of such freeway designs. Eight existing, two under-construction, and one approved-for-construction freeway sections have been studied on a before-, during-, and after-construction basis. The sections selected for study range from being in predominately residential suburban areas to predominantly commercial-industrial downtown areas. The specific effects of the three types estimated for each study section are as follows: (1) social impacts: population changes, neighborhood accessibility, neighborhood cohesion and community services; (2) economic impacts: relocation and mitigation costs, business sales, property uses and values, tax revenues, employment, and income and user costs; and (3) environmental impacts: aesthetics, drainage and erosion, noise and air pollution, vibration and hazardous spills. The literature review and a survey of highway agencies in other states were used to determine the appropriate procedures or models and mitigation measures to implement in estimating the social, economic, and environmental impacts of elevated and depressed freeways. The results of the study, presented in six separate reports according to types of effect, can be used by highway planning and design engineers to prepare environmental statements and documents of the expected social, economic, and environmental impacts of proposed elevated and depressed freeway projects. Also, the results can be disseminated at the public hearings for a proposed project. This report presents the findings of the traffic noise effects of elevated, depressed, and at-grade level freeways. In summary, it was found that the depressed freeway sections provide the greatest reduction of traffic noise in areas near and far from the roadway, especially if the walls of the depression are sloped or acoustically treated. The next best condition is an elevated freeway section using solid concrete guardrails. The traffic noise is shielded by the solid deck and rails. The reduction is measurable near the elevated section, but at greater lateral distances, away from the roadway, levels approach those of at-grade roads because all traffic is not shielded by the deck and rail. At-grade roads produce the highest noise levels, but the addition of solid guardrails, median rails, and the use of smooth texture pavements provide noticeable quieting.