Researchers Used Microsimulation Models to Fine-Tune and Assess a Variable Speed Limit Control Strategy for the Evening Peak Period on I-285 in Georgia.
Dekalb County, Georgia, United States
Implementation of a Variable Speed Limit/Ramp Metering Strategy to Increase Freeway Capacity at Metered On-Ramps
Summary Information
In an effort to avoid the capacity drop phenomenon at freeway merge bottlenecks, researchers proposed an algorithm, named TORBO, which combined Variable Speed Limit (VSL) and ramp metering (RM) strategies to increase capacity. This strategy uses detector data to identify ramp queue spill-back and activate VSL in response on the shoulder lane approaching the merge section. This VSL-RM strategy was optimized and assessed using data from two locations, the Memorial Drive and Chamblee Tucker Road ramps on I-285 surrounding Atlanta, GA.
Methodology
The GTsim microsimulation package was used in the analysis along with one month of traffic data (volume, speed, and occupancy at 20-second intervals) from February 2019 from Georgia Department of Transportation’s NaviGAtor Vehicle Detection System and 48 hours of ramp volume data at five-minute intervals. After optimizing the algorithm parameters, three scenarios were analyzed with respect to travel time, measured in vehicle-hours, for the overall system as well as the ramp traffic and freeway traffic separately:
- No control
- RM control only
- VSL-RM control
Findings
The changes in travel time from the no controls scenario are shown in Table 1 for both the Memorial Drive and Chamblee Tucker Road locations.
- Both the RM and VSL-RM scenarios include ramp metering, resulting in reduced travel time for the freeway traffic but much higher travel times for the ramp traffic.
- Overall, system travel time with RM control only was 1.5-1.7% lower than in the no controls scenario. Overall travel time for system traffic with VSL-RM control was 3.4-4.4% lower than the no controls scenario.
Table 1: Travel time changes (percentage change vs. no controls) for studied scenarios
|
|
RM Only |
VSL-RM |
|
Freeway Traffic (Memorial Drive) |
-12.2% |
-13.2% |
|
Freeway Traffic (Chamblee Tucker Road) |
-7.6% |
-10.4% |
|
Ramp Traffic (Memorial Drive) |
+83.1% |
+66.8% |
|
Ramp Traffic (Chamblee Tucker Road) |
+113.2% |
+116.1% |
|
Overall System (Memorial Drive) |
-1.7% |
-4.4% |
|
Overall System (Chamblee Tucker Road) |
-1.5% |
-3.4% |
