Assessing the air quality impacts of the traffic signal coordination projects: A modal approach

Although traffic signal coordination projects have been widely implemented to relieve traffic congestion, their air quality impacts have never been clearly demonstrated and have become the subject of much discussion and debate. The USEPA has stated that "the emissions effects of (traffic signalization projects) can be difficult to quantify." As a result, much concern exists among transportation and air quality professionals regarding the ability of current approaches to provide the degree of reliability desired.; Another concern regarding the air quality impacts of traffic signal coordination projects involves the tradeoffs between possible increases in nitrogen oxide (NO{dollar}rmsb{lcub}x{rcub}){dollar} emissions which are predicted using current approaches, and reductions in carbon monoxide (CO) and hydrocarbon (HC) emissions.; This dissertation research resulted in the development of a new modal approach for assessing the air quality impacts of traffic signal coordination projects. The two greatest improvements over current approaches include: (1) Modal approach: Research has demonstrated that modal vehicle events (i.e. acceleration, deceleration) can and do significantly impact vehicle emissions. Approaches which average speeds disregard modal events. (2) Microscale framework: USEPA's MOBILE model was intended for regional emissions inventories and was never intended to be used to assess the air quality impacts of microscale transportation projects.; The developed approach was applied to two case study arterials. Speed profiles were collected before and after project implementation to measure changes in modal variables and emissions were computed using new EPA modal models. The results for the two cases indicate that traffic signal coordination projects can reduce NO{dollar}rmsb{lcub}x{rcub}{dollar} emissions as well as HC and CO emissions. While the potential for these projects to reduce NO{dollar}rmsb{lcub}x{rcub}{dollar} emissions has long been acknowledged in the transportation air quality community, this potential could not be demonstrated until now.; The research findings indicate that the modal approach is an improved approach for assessing the air quality impacts of traffic signal coordination projects. Use of the modal model is recommended.