1174898 - Estimating Emission Benefits of Electronic Open-Road Tolling Conversion Projects

Intelligent transportation systems using vehicle-to-infrastructure communications are being adopted rapidly. Many state and local transportation agencies are currently evaluating the replacement of highway toll plazas with open-road (or overhead) gantries, often mounted with high-resolution cameras for license plate reading and high-speed sensors for transponder detection. Conversion to electronic open-road tolling (EORT) systems can provide a range of benefits, including smoother traffic flow and lower crash risk, better asset management and lower maintenance costs, and the ability to instantaneously adjust fares for variable or congestion pricing. EORT systems can also potentially reduce emissions and energy consumption; however, the environmental benefits between different electronic tolling configurations have not yet been well-characterized.

The goal of this study was to estimate emission and energy reductions for EORT conversion projects to support development of a new tool in the Federal Highway Administration’s (FHWA) Congestion Mitigation and Air Quality Improvement (CMAQ) Emissions Calculator Toolkit. A three-tiered approach was applied, utilizing real-world traffic volume and speed data from two Interstate 90 toll facilities near Boston before and after EORT conversion. First, traffic microsimulations of different tolling configurations were run to generate vehicle operating mode distributions to represent driving behavior through toll facilities. Second, operating mode distributions were used as project-level inputs in the U.S. Environmental Protection Agency’s Motor Vehicle Emission Simulator (MOVES). Finally, multivariable linear regressions were developed to estimate emissions and energy for traffic conditions not explicitly modeled.

Findings from this study show that EORT systems allow for higher average speeds during peak commuting hours and traffic to achieve free flow conditions during nonpeak hours. Mainline traffic throughput typically also increases after converting to EORT facilities from full stop or rolling cruise (i.e., 5-15 mph) toll plazas. MOVES modeling consistently demonstrated larger emissions and energy benefits for conversion of full stop toll plazas to EORT compared with conversion of rolling cruise tolls. For passenger vehicles on a per mile basis, full stop conversions were found to reduce fine particulate matter (PM2.5) up to 61% and energy consumption up to 28%, whereas rolling cruise conversions reduced PM2.5 up to 34% and energy consumption up to 10%. These findings help confirm the emission benefits and fuel savings of converting legacy toll plazas to open-road systems.