Between Dec 19, 2024 and Jan 2, 2025, datasets can be submitted to DRUM but will not be processed until after the break. Staff will not be available to answer email during this period, and will not be able to provide DOIs until after Jan 2. If you are in need of a DOI during this period, consider Dryad or OpenICPSR. Submission responses to the UDC may also be delayed during this time.

Browsing by Author "Sheikh, Atif"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Measuring the Equity and Efficiency of Ramp Meters
    (2004-11-01) Levinson, David M; Zhang, Lei; Sheikh, Atif
    Traffic congestion has become an increasingly serious problem in many cities. Ramp metering, which maintains smooth freeway mainline flow by limiting vehicle entry at entrance ramps, has been proposed and implemented in a number of metropolitan areas in and outside the U.S. to mitigate freeway congestion. This study aims to develop both efficient and equitable freeway ramp control strategies. Traffic conditions with and without ramp metering are evaluated on several representative freeways in the Twin Cities with a comprehensive set of performance measures. A unified theory for ramp metering is proposed based on a linear programming model of freeway traffic dynamics. The most efficient ramp control algorithm is found to be also the least equitable one. A novel control objective, minimizing weighted or perceived travel time, is therefore proposed to balance efficiency and equity objectives of ramp metering. This research also develops a new family of applicable ramp metering strategies, which consider both efficiency and equity, and are demonstrated in a microscopic traffic simulator. Future studies should compare various traffic control methods under the analytical framework proposed in this report. Researchers should also pursue field experiments of the proposed multi-objective ramp control strategies.
  • Thumbnail Image
    Item
    Traffic Equilibration: The Case of the Twin Cities Ramp Meter Shut Off
    (American Society of Civil Engineers, 2002) Levinson, David M; Sheikh, Atif
    In Fall 2000, more than 430 ramp meters in the Twin Cities metropolitan area were shut down in order to evaluate the effectiveness of the metering system. This shutdown disturbed normal traffic patterns and thus traffic equilibrium. The purpose of our research is to examine how long it takes to establish a new equilibrium after a shock to the system, and thus establish the basis for how long these traffic studies should be carried out, as transportation analysts are generally concerned with comparing two equilibrium conditions. The initial results contradict our hypothesis that as the number of weeks since the shutdown increases, the week-to-week change in volume decreases. In fact our results show that not only are the week-to-week changes in volume is greater for shutdown case than for pre-shutdown case, those changes are rising as the experiment proceeded. More research is needed to examine the question of whether and how equilibria form, and we need to examine longer time slices for analysis to consider alternative definitions of equilibria.