Impacts Of Signal Synchronization On Vehicular Emissions - An On-board Measurement Case Study

Nearly 56% of total nitrogen oxide (NOx) emissions are produced by mobile sources. Transportation and air quality managers at the state and regional level have the responsibility of developing and evaluating Transportation Control Measures (TCMs) and Transportation Improvement Plans (TIPs) to improve air quality of the region. Signal synchronization is considered to be an effective TCM to reduce corridor congestion and maintain air quality in the region. This research was carried to determine the impacts of signal synchronization on real-world, on-road emissions. A portable instrument, OBS-1300 manufactured by Horiba Instruments Inc., was used to measure on-road tailpipe emissions of NOx on a second-by-second basis during actual driving. Data was collected in a light-duty 1999 Chevy Astro van. The focus of data collection was measuring emissions before and after signal synchronization on Great Southwest Parkway, Grand Prairie, Texas. The collected data was analyzed by a series of statistical tests. The results determine that there is no significant change in NOx emissions after signal retiming. Therefore, various variables were analyzed to check for their effect on emissions. It was observed that with the signal retiming, the average speed increased, which is directly proportional to NOx emissions. Also, the parameters like ambient temperature, driver behavior, peak conditions and days of the week significantly impact real-world NOx emissions. The instantaneous model also indicated that engine parameters significantly impact NOx emissions in addition to instantaneous velocity and acceleration. Thus, on-board data demonstrate the importance of real-world conditions and help develop more accurate traffic and air quality management policies.