Develop tools and procedures to model impacts of near-road barriers on near-road pollutant concentrations

Focus Area

Air Quality


Air Quality






1-2 years

Research Idea Scope

RESEARCH PROBLEM STATEMENT Interstate highway improvement projects that are deemed to have traffic noise impacts result in near-road barrier walls being constructed or expanded. Although the barriers are designed and constructed for noise abatement purposes, studies have shown that these walls can alter the near roadway dispersion characteristics. This project aims at collecting data from available ambient monitoring studies upwind and downwind of noise barrier walls, and use this information along with street canyon (or other appropriate dispersion) models to develop improved near roadway project-level dispersion modeling analyses. The results from this study will provide practitioners/users with tools to incorporate near roadway characteristics (including terrain features other than walls) in Environmental Protection Agency (EPA) approved dispersion models (AERMOD or CAL3QHC/R) to estimates of downwind criteria and toxic air pollutant concentrations. BACKGROUND Numerous studies have shown that air pollution increases the risk of different diseases. Moreover, effects of long-term exposure to air pollution have been proven to cause different health issues (Harrison et al., 1999; Perry et al., 2005; Wilhelm & Ritz, 2003). Vehicles account for a large share of pollutant emissions in urban areas. Vehicles account for a large share of pollutant emissions in urban areas. Studies have shown that people living in near-roadway communities (within 100m of the road) are exposed to the noise and high concentrations, which may be associated with adverse health effects. Many studies have been conducted to investigate the effects of sound wall barriers and vegetation near the roadways on vehicular pollutant dispersion via experimental or numerical approaches. According to these studies, sound wall barriers are capable of reducing downwind pollutant concentrations between 15 and 50%; however, in some specific wind directions, concentration of pollutants were found to increase compared to cases without the wall (Baldauf et al., 2008; Bowker et al., 2007; Finn et al., 2010; Heist et al., 2009; Mao et al., 2013; Speckart & Pardyjak, 2014). While studies exhibit promising benefits from installing near-road barriers, the effects are still uncertain (EPA, 2015). The effectiveness of sound walls at mitigating near-road pollution exposure depends on roadway configuration, local meteorology, and barrier height, design, and endpoint location. Similar to sound walls, concentrations may be higher behind a vegetative barrier that is located downwind of the roadway if there are gaps in the vegetation such as missing or dead trees, or lack of cover from the ground to the top of the vegetation (EPA, 2015). Models for quantifying impacts are still under development EPA and FHWA approved models for air quality modeling purposes (AERMOD and CAL3QHC/R) currently lack the ability to model the effects of near-road barriers. This ; results in reducing the capability of the model in developing feasible solutions to mitigate air pollutant concentrations in near-roadways areas. Adding a feature to the AERMOD to consider near-roadway barriers , like what R-Line currently has, enhances the accuracy of model and will aid in decision making process for EPA, FHWA, and state DOTs. According to FHWA inventory of noise barrier walls, constructed noise barrier walls nationwide exceeded 2700 linear miles at a cost of over $5.4 billion through the end of 2010 (FHWA-HEP-12-044). State DOT’s will continue to use near-road barriers as an important tool to reduce the impacts of traffic noise that result from the ongoing improvement of highways. So it is important to identify the effects on noise barrier on near-roadway pollutant concentration. RESEARCH OBJECTIVES 1. Identify and review key studies which have ambient pollutant concentrations measured at sites with nearby near-road barriers. 2. Evaluate the effect of barriers on near-roadway ambient concentrations using the data sets identified in Task 1. 3. Use the Task 2 results; develop algorithms that can be used in line source emission and dispersion modeling applications to estimate the effects on concentrations upwind and downwind of near-road barriers. 4. Incorporate algorithms in guideline models like AERMOD, CAL3QHC/R that can be made available to transportation and air quality practitioners 5. Develop guidance on using AERMOD, CAL3QHC/R for analyzing transportation projects with barriers 6. Document all work in a concise final report

Urgency and Payoff

1. Availability of near-road barrier walls as a modeling option in AERMOD and CAL3QHC/R enables policy makers and practitioners to assess the effectiveness of barrier walls in reducing near-road pollutant concentration estimates. 2. Achieve higher accuracy in modeling and obtaining realistic results of exposure assessment for transportation projects. 3. Accurate dispersion modeling by incorporating near-road barrier modules can refine the project-level conformity analysis results. 4. Capability of these structures in mitigation of near-roadway transportation-related air pollution (TRAP) can be considered for FHWA’s “Feasibility” analysis for noise.

Suggested By

Suriya Vallamsundar Texas A&M Transportation Institute 9729942209

[email protected]