Vehicle Emissions and Traffic Measures: Exploratory Analysis of Field Observations at Signalized Arterials

Understanding the relation between vehicle emissions and traffic control measures is an important step toward reducing the potential for global warming, smog, ozone depletion, and respiratory illness. Traffic analysts, through improved roadway design and traffic control, have the ability to reduce vehicle emissions. However, current vehicle emissions models do not allow traffic analysts to easily and accurately predict vehicle emissions based on commonly used traffic measures. The primary purpose of this exploratory research is to study the effects of traffic flow on real-world vehicle emissions. The rates of vehicle emissions are evaluated during each “mode” of travel: acceleration, deceleration, cruise, and idle. Then, the relationship between vehicle emissions and a commonly used traffic measure, control delay, is investigated. Data for this research were collected in real-time through the use of a portable, On-board Emission Measurement unit (OEM 2100). The OEM 2100 allows real-time, field data collection of second-by-second measurement of tailpipe emissions (i.e., CO, HC, and NO) and engine operations (i.e., speed and engine rpm). This is the first research project deploying the OEM 2100 and differs from the majority of past emissions research in focusing on the collection of real-world, on-road data from instrumented vehicles. A key result from this study is that vehicle emissions were found to be highest during the acceleration mode and lowest during the idling mode. Also, vehicle emissions were found to be approximately twice as much during control delay than when not in delay. This is because acceleration events often occur within control delay events.