Abstract
On-ramps and off-ramps that serve as connections between high-speed facilities and arterials are potential hotspots for vehicle emissions. The engine load associated with grade and acceleration on uphill ramps can lead to significant emissions of criteria pollutants and greenhouse gases (GHGs) over a short distance. This study explores transit bus operations and emissions at ramps using Global Positioning System (GPS) data collected from Detroit transit buses. Ramp-associated operating data are extracted from the vehicle traces using ArcGIS and assigned to the applicable United States Environmental Protection Agency’s emission rates, i.e., EPA’s Motor Vehicle Emission Simulator (MOVES). The results show that transit bus emission rates for on-ramp operations at 40 mph (64.37 km/h) are about double the average emission rate on the MOVES highway cycles. For lower on-ramp speeds (< 64.37 km/h), as average speeds decrease, on-ramp emission rates drop roughly to the highway emission rates given the less aggressive acceleration noted in the data. Off-ramp emission rates are approximately half of the highway emission rates. The study also finds that post-ramp acceleration, right after buses enter the highway from the on-ramp, contributes to high emissions, because of the high-speed and high-power operations. This is true for the loop on-ramp, where the bus emission rate after entering the highway is higher than the emissions associated with driving on the ramp. On-ramp emissions are found to vary across a wide range of conditions, indicating that further study and more data are needed to explore the overall impacts of on-ramp and post-ramp activity in emissions modeling. A sensitivity analysis of ramp grade effect on emission indicates that ramp grade should be specifically considered in project-level analyses. The research results are useful for understanding ramp driving characteristics, the potential impacts of ramp grade on emissions, and the ramp hotspot analysis.
Highlights
The ramp acts as a connection between highways and local roads
The Motor Vehicle Emission Simulator (MOVES), the regulatory emission model invented by the U.S Environmental Protection Agency [1], defines ramp activity as vehicle operations that occur between the unrestricted road and the restricted road
MOVES assumes that ramp activity comprises about 8% of nationwide freeway operating hours for all source types [1], based upon the ramp fraction value originally developed by Systems Applications International, Inc. for the MOBILE model [2]
Summary
The ramp acts as a connection between highways and local roads. Significant differences in operating conditions exist between the roadway facilities that ramps connect, in terms of speed, elevation, and roadway configuration. The Motor Vehicle Emission Simulator (MOVES), the regulatory emission model invented by the U.S Environmental Protection Agency [1], defines ramp activity as vehicle operations that occur between the unrestricted road (local road) and the restricted road (highway/freeway). The research presented in this paper assesses the observed on-road operations and modeled emissions of transit bus activity on-ramps. Research results are useful for understanding transit bus operations and emission characteristics on various types of ramps, the potential impacts of ramp grade on emissions, and the ramp hotspot analysis.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
