Tailpipe emissions significantly contribute to air quality problems at both local and regional scales. The quantity of tailpipe emissions is affected by several factors including vehicle characteristics, driver behavior and prevailing road and traffic conditions. This paper presents a corridor-level methodology to compare tailpipe emissions produced at a site in Raleigh, North Carolina, where a Transportation Improvement Project (TIP) was implemented to convert a traffic signal to a multi-lane roundabout in 2010. An intersection-level analysis is also presented to assess the contribution of the multi-lane roundabout to the emissions impacts of the TIP. It is common in practice to synthesize or forecast traffic activity data and use it to predict the traffic emission impacts and compare changes before and after a TIP. The unique methodology in this paper presents an alternative to forecasting, by utilizing empirical emissions and vehicle activity data collected before and after the TIP. Second-by-second tailpipe emissions concentrations were collected via a Portable Emissions Measurement System (PEMS), which was installed in the test vehicles. Emissions factors were obtained and used with vehicle activity before and after the TIP. It was found that at the corridor-level, turning movements from the main street produced higher total emissions while turning movements from the minor street produced lower total emissions after the TIP. The emissions per unit distance were lower for most movements after the TIP. However, these differences were not statistically significant. At the intersection-level, two movements that were made directly at the study intersection showed that vehicles tested after the TIP at the multi-lane roundabout had lower emissions per unit distance. For the right turn from the minor street to the major street, the decrease in emissions per unit distance of carbon monoxide, hydrocarbons and carbon dioxide was significant.
↧