In Glasgow, Scotland a freeway ramp metering system installed at an entrance ramp to the M8 motorway reduced the frequency of early merging by 29 percent.
The ramp meter evaluated during this project, on an entrance ramp to the M8 motorway, was implemented to address a PM peak congestion problem. The meter is activated by heavy traffic volume on the freeway, however, and could be activated at anytime. During periods of ramp meter operation or, in extreme cases, ramp closure, traffic signal timings on the adjacent arterial adjust to accommodate additional volume traveling to the next downstream freeway entrance.
The project used video from two traffic cameras, one upstream of the ramp and one downstream, to assess the safety improvement gained through the ramp meter. An automated analysis system identified corner features in the video image and tracked their motion through the frame. Movement of these corner features allowed the determination of percentage of vehicles merging early, the percentage of vehicles changing lanes in the two lanes adjacent to the ramp within the area immediately prior to the merge area, and the mean deceleration of vehicles entering the merge area. Due to the positioning of the cameras, aggregating the corner features to identify individual vehicles was not possible.
Findings from the study indicate that the number of vehicles merging too early decreased after the implementation of ramp metering, from 35 percent to 25 percent. The study also found that the amount of lane changing in the two lanes adjacent to the ramp appears to have dropped. Prior to implementation, the percentage of vehicles changing lanes in this area ranged from 6 to 15 percent, while after ramp metering began this number ranged from 1 to 8 prcent. The swaying of the camera towers and their distance from the merge area lead to artificially high measured speeds for slow moving vehicles. This prevented quantitative measurement of vehicle deceleration. Qualitative analysis indicates that mean speed changes during ramp metering appear smaller than prior to implementation, but the authors stress that additional analysis is required for a quantitative determination.
Tarry, Steve and Martin Pyne. UK-M8 Motorway Ramp Metering (TABASCO Project). European Commission Directorate General Energy and Transportation, TEMPO Secretariat, (Document No. SW0203). 13 February 2003.
Safety Evaluation of Ramp Metering in Glasgow Using the Asset Image Processing System
Author: Allsopp, Richard, et al.
Published By: Paper presented at the 5th World Congress Conference on ITS. Seoul, Korea
Source Date: 12-16 October 1998
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