2258 - Impact of Different Ramp Metering Strategies on Vehicle Emissions along Freeway Segments

Abstract

2nd Highest Scoring Abstract: Undergraduate/Masters Background Air pollutants are widely recognized as the substances that adversely affect the global climate, plants and animal species and public health. Certain strategies have been proposed to reduce vehicle emissions, such as the ecology oriented pavement designs and green road operations. A ramp meter is typically installed on a freeway entrance ramp to regulate the traffic flow entering a freeway according to actual traffic conditions. Ramp meters could reduce traffic congestion through adjusting ramp traffic flows to minimize the disruptions on mainline traffic flows. While there is plenty of mobility and safety related research on ramp metering, there are relatively fewer studies on the estimation of specific impacts of ramp metering on freeway emissions. Methods The objective of this research is to estimate emissions while driving along mainline freeways with a series of ramps that are controlled by meters. The vehicle emissions were estimated based on the instant vehicle speed and acceleration rate through dynamic vehicle operating modes defined by EPA MOVES. Real time driving speed and acceleration rate were measured from a test vehicle driving along the freeway I-45 in Houston, TX, where five on-ramps were placed with three control mode: (1) no metering, (2) isolated metering, and (3) integrated metering. Results During rush hours of a weekday, the isolated and integrated ramp metering strategies could improve the mobility, therefore reducing travel delay; and prevent harder acceleration and deceleration from being operated. The integrated metering strategy is more beneficial to the mobility improvement and smooth vehicle maneuver than the isolated one, which is reflected by the dominant distribution of the operational mode IDs as well. However, the ramp metering control strategy is not always favorable to vehicle emissions. The total mainline freeway emissions estimated under the isolated ramp metering strategy are higher than the no metering strategy. Conclusions Isolated and integrated ramp metering control strategies could improve mobility and enhance smooth vehicle maneuver in the mainline of a freeway. In the mean time, only when the mobility is significantly improved, such as the one in the integrated ramp metering control strategy, the total emissions are tremendously reduced for the shorter emission duration. Therefore, the integrated ramp metering control strategy is superior to the isolated control strategy, in terms of both mobility and vehicle emissions.