A simulation study in Minneapolis-St. Paul estimated that ramp metering saved 2 to 55 percent of the fuel expended at each ramp.
The model was built around the AIMSUN (Advanced Interactive Microscopic Simulator for Urban and Non-Urban Networks) model, and was designed to emulate traffic conditions based on data collected from traffic detectors in the Twin Cities. In addition, the simulation was able to modify ramp meter timings and compensate for congested conditions in real-time by predicting driver behavior and estimating impacts of traveler information on traffic conditions.
The integrated ramp meter control strategy was designed to handle freeway zones with unidirectional links extending 3 to 6 miles in length. The zone of influence for each ramp included the upstream free-flow area (e.g. low incident area) and the downstream bottleneck area (e.g., lane drop areas, high volume entrance ramps, and weaving areas). The control algorithm was designed to balance the volume of traffic entering and leaving each zone every 30 seconds. When the density of vehicles decreased, additional capacity was recognized.
In order to develop a model that would accurately reflect the geographical setting at each ramp, a graphical-editor for traffic networks was used to create an individual zone of influence for each ramp meter. The graphical editor accepted spatial data from computer drafting programs or aerial photographs and facilitated the placement of nodes in a model network. Once the ramp meter network was integrated into AIMSUN, traffic detector data was loaded as model input. The input consisted of field data (5-minute volume and occupancy measurements) collected from 3000 TMC Mn/DOT detectors, and manual traffic counts determined from cameras and on-site observations. Conditions at model boundary areas were determined through manual counts at TH-169 and I-94. All data represented incident free conditions between 2:00 PM to 8:00 PM.
Ramp metering reduced the number of acceleration-deceleration cycles and smoothed traffic flow. Fuel savings at each ramp meter ranged from 2 to 55 percent depending on ramp roadway geometry and daily fluctuations in demand.
Twin Cities Ramp Meter Evaluation: Phase I Report
Mn/DOT Ramp Meter Evaluation: Phase II Report
Evaluation of Ramp Meter Control Effectiveness in Two Twin Cities Freeways
Author: Hourdakis, John and Panos Michalopoulos
Published By: Paper presented at the 81st Annual Transportation Research Board Meeting. Washington, District of Columbia
Source Date: 13-17 January 2002
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