Measuring the Equity and Efficiency of Ramp Meters

The general purpose of this study is to develop both efficient and equitable freeway ramp control strategies. Measures of efficiency and equity for ramp meters are defined and applied to data collected in the Twin Cities ramp metering shut-off experiment. A trade-off between efficiency and equity is evident from the results of data analysis. A new time-dependent optimization program for the global optimal ramp control problem is developed, which aims to minimize total travel time and does not require origin-destination demand information. A heuristic solution to the real-time version of the new optimization program is also provided which can be directly implemented in real-world freeway networks. The heuristic provides a qualitative foundation for the development of an analytical framework for ramp metering under which future ramp metering studies can be conducted. In addition, a new series of ramp control strategies, Co_EOAX, is developed based on the heuristic with some additional equity considerations. Since the metering objective of minimizing absolute travel time is purely efficiency-oriented, a new objective for ramp metering, minimizing weighted (perceived) travel time, is presented, which has equity considerations built in when ramp delays are weighted non-linearly. A simulate method to achieve this new metering objective is also developed which is able to balance efficiency and equity of ramp control strategies. Co_EOAX is coded and tested in a microscopic traffic simulator and the optimal equity consideration in Co_EOAX is identified by the new metering objective. Finally, it is shown in the simulator that the Co_EOAX with the optimal equity consideration is both more efficient and more equitable than the no-control scenario and an exiting ramp control strategies.