In this study novel methods have been used for evaluating strategies aimed at preventing motor vehicle air pollutant emissions through better traffic management. Actual on-road emissions measurements were utilized in contrast to the laboratory-based dynamometer tests employed in many current projects. The primary objectives of this research were to:
- Assemble, evaluate, and validate a new low-cost on-board emissions measurement (OEM-2100TM) system;
- Investigate factors that affect the level and variability of on-road emissions using rigorous statistical methods;
- Devise methods for designing and conducting experiments that realistically evaluate vehicle-based pollution prevention strategies.
Objective (1) was satisfied via the procurement of two OEM-2100TM portable on-road tailpipe emissions measurement systems. Objective (2) was satisfied by developing a data collection protocol, collecting on-road emissions data, and analyzing the data using graphical, statistical, and theoretical approaches. Objective (3) was satisfied by designing and conducting a real-world emissions measurement study before and after the implementation of changes to signal timing and coordination on two separate study corridors.
The project proceeded in two major phases. The first, or pilot, phase, involved preliminary deployment of the OEM-2100TM with specific vehicle, driver, route, and scheduling combinations for purposes of developing data collection and reduction protocols and to develop a preliminary database for use in identifying potentially important factors influencing emissions. Based upon the lessons learned in the pilot phase, an experimental design was developed for the second, or evaluation, phase of the project. The evaluation phase focused on detailed evaluation of the change in vehicle movement and emissions associated with a change in signal timing and coordination on two corridors, each approximately two miles long.
The specific pollution prevention strategy evaluated in this project was modification of signal timing and coordination as a means to improve traffic flow. The pollutants studied include carbon monoxide (CO), nitric oxide (NO), and hydrocarbons (HC). A hypothesis that motivated this project is that vehicle emissions are sensitive to micro-scale events that occur during a trip or along a specific corridor. Such events, such as accelerations at intersections, may cause relatively high emission rates. Therefore, efforts to smooth traffic flow by improving signal timing and coordination may lead to a reduction in the number of accelerations and, hence, lead to reductions in emissions.
Portable instruments were used for measuring carbon monoxide (CO), nitric oxide (NO), and hydrocarbon (HC) emissions and vehicle activity (e.g., vehicle speed, engine parameters) on a second-by-second basis. Data collection, quality assurance, reduction, and analysis protocols were developed. Field data collection occurred in a pilot and an evaluation phase. In total, over 1,200 one-way trips were made with more than 20 vehicles, 4,000 vehicle-miles traveled, 160 hours of data, and 10 drivers. The pilot study was used to identify key factors influencing on-road emissions and as input to the design of the evaluation study. In the evaluation study, data were collected intensively with a small number of vehicles on two corridors before and after signal timing and coordination changes were implemented.