The effect of roadway configurations on the dispersion of traffic-related pollution: a wind tunnel study

In this paper we examine the effect of different roadway configurations, including noise barriers and roadway elevation or depression relative to the surrounding terrain, on the dispersion of traffic-related pollutants for winds perpendicular to the roadway. A wind tunnel experiment modeling 12 different configurations was performed to study the flow fields and the concentration distributions resulting from emissions from a simulated six-lane highway. All of the configurations examined here reduced the downwind ground-level concentrations relative to that for a flat, unobstructed roadway; however, the degree to which the concentrations were reduced varied widely depending on the particular situation. These experiments confirm the utility of the vertical entrainment velocity in characterizing the rate of concentration decrease with downwind distance from the road. This parameter previously has been found useful in modeling ground-level releases and has been used particularly in hazardous release models. Ground-level concentration data from the cases considered in this research indicate that a constant entrainment velocity can be used over the region beginning downwind of any initial disturbance to the flow resulting from the roadway