Seeing a smoking vehicle traveling down the highway makes us think about the air we’re breathing. When rainfall causes the road to be slick from tire residue and engine spills, we don’t often think of what happens when the pollutants wash off the road. But what the roadside does with the polluted water and how well we monitor and curtail air pollution coming from vehicle emissions are two areas very important to Environmental Protection Agency (EPA) regulators, the Texas Department of Transportation (TxDOT) and the Texas Commission on Environmental Quality.
“The roadside is more than just something pretty to look at. It’s a mini-ecosystem with environmental functions that provide storm water treatment and habitat that can be maximized through proper design and maintenance activities,” says Beverly Storey, associate research scientist.
Off the pavement, researchers consider the right-of-way as green infrastructure with benefits for water quality, vegetation, aesthetics and landscape development. EPA recently implemented new effluent limits that determine how dirty the water can be as it drains from construction sites. In response to the upcoming regulations, Storey’s team will work with Texas Tech University and The University of Texas Center for Transportation Research testing roadway construction site storm water discharges to develop site-monitoring protocols for TxDOT.
TTI Associate Research Engineer and Texas A&M Associate Professor of Landscape Architecture Ming-Han Li recently built the first bioretention pond at the corner of State Highways 6 and 21 for a TxDOT field study. This green storm water runoff management practice reduces the size of right-of-way necessary for TxDOT while being more aesthetically pleasing than the traditional, large concrete drainage structures. Based on pilot experiments with vegetation planted in recycled trash dumpsters, researchers believe the field test will show that bioretention ponds effectively remove pollutants — such as copper, zinc and lead — from storm water runoff.
Cleaning the Air…with Earth?
Meanwhile, the dumpsters from Li’s pilot test are being reused again for a Southwest University Transportation Center project. The fully vegetated dumpsters will be fitted with lights for photosynthesis and placed in TTI’s new Environmental and Emissions Research Facility (EERF; see related story) for a controlled study on how vegetation and soil can remove pollutants and emissions from the air under different temperatures.
Inside the chamber, emissions will bombard the vegetation and soil. Storey’s team is excited about measuring how much carbon gets captured and developing protocols for further laboratory tests on specific plant species and soil types. With these protocols, researchers hope to find more green solutions to air quality challenges using vegetated roadsides.
Modeling: An Air of Refinement
Complying with all state and federal air quality standards requires some detailed analyses that cannot be physically measured. Advanced computer modeling using EPA’s emissions estimation software, called Motor Vehicle Emissions Simulator (MOVES), helps metropolitan planning organizations demonstrate that building new transportation structures will conform to air quality standards. TTI’s Transportation Modeling Program, led by Dennis Perkinson, approximates levels of pollutant concentrations by area all over the state. Perkinson’s team constantly updates and improves the MOVES model as new products and variables become available — new measurements that could possibly come from EERF projects.
“The mathematical model takes many variables — emissions from 28 types of vehicles over 25 model years, links of road, every hour of the day, given speed of each link per hour, types of pollutants and even fuel types,” says Perkinson. “If you change a network or build something new, you need to be able to calculate the impact for the regulators. Our group’s innovations are extremely efficient protocols and procedures for doing this, for almost the entire state.”
As EPA standards evolve, the sophistication of the environmental research methods necessary to test for them also change. More refined measures, new controlled laboratory studies and behind-the-scenes computer modeling make a huge impact. In short, TTI research helps all Texans breathe a little easier.