Projects Publications

Quantifying the effects of land-use and socio-economics on the generation of traffic emissions and individual exposure to air pollution at a metropolitan scale

This study investigates the isolated and combined effects of network congestion, roadway grade, passenger load, and fuel type on transit bus emissions of greenhouse gases (GHG) through a simulation of transit operations and emissions along a busy corridor. We also test the effect of changing random seed on the overall corridor emissions. We observe that positive grades have strong effects on emissions as well as cause other variables to become significant such as passenger load. The effects of increasing negative grades on emissions are often offset by varying the random seed in the traffic simulation. While an increasing passenger load on the bus also increases bus emissions, we observe that the addition of each passenger influences the per-passenger emissions differently depending on the bus occupancy level. Finally, the reduction potential of compressed natural gas (CNG) was found to vary across different network speeds, grades, and passenger loadings.

Graph representing the effect of varying passenger load on total and per passenger GHG emissions
The effects of varying passenger load on total and per passenger GHG emissions. This figure illustrates how the addition of every passenger impacts emissions as a total and on a per passenger basis. When the number of passengers increases from 0 to 76, the bus emission factor increases from 975 g/mile to 1,160 g/mile, an increase of 18.97% (at zero grade and average bus speed of 16.29 mph). But if emissions are considered on a per passenger basis, then an opposite trend is observed. For the same passenger increase from 0 to 76, the emission factor per passenger changes from 974 g/mile.pass to 14 g/mile.pass, a decrease of 98.56%. The reduction in per passenger emissions is high when the bus is less occupied and as the number of onboard passengers exceeds the seating capacity of the bus (PLF>1.0), the benefit of adding passengers starts to decrease.