Effects of traffic signal re-timing on vehicular nitrogen oxide emissions

Vehicular emissions are a major source of nitrogen oxide emissions, which is formed due to a spontaneous reaction between nitrogen and molecular oxygen at high temperatures. The Dallas/Fort-Worth Metroplex is a NOx-limited region and is designated as "nonattainment" for tropospheric ozone.; In this research, traffic-signal retiming was considered as the primary transportation control measure and its beneficial aspects evaluated by means of rigorous data collection, and statistical analysis. On-board emissions measurement was employed using the OBS-1300 and MEXA-720-NOx systems manufactured by Horiba Instruments, Inc. The corridor taken into consideration for this research was Cooper Street situated in Arlington, Texas. This corridor carries high traffic volumes due to the location of UTA and various other businesses such as the Parks Mall and WalMart. The instruments were installed into a 2000 model year Chevrolet Astro van, a university fleet vehicle. Runs were made before and after traffic-signal retiming for predicting variations in the NOx emission factors. Parameters such as time of day, day of week, direction of run, and driver behavior were taken into consideration. After the completion of data analysis using statistical methods such as the analysis of variance, and hypothesis testing with t-distribution, a statistically significant decrease in NOx emissions of 36.1% in the peak hours between 7 a.m. to 9 a.m. and 4 p.m. to 6.30 p.m., and 28.4% in the off-peak hours between 9 a.m. to 4 p.m. was observed.; The results that were obtained suggest that traffic-signal retiming is an effective transportation control measure, which may provide significant decreases in NOx emissions on many other similar corridors.