Identifying and Prototyping Integrated Corridor Management (ICM) Strategies for Application in Virginia
This study focused on a comprehensive ICM approach as opposed to traditional measures that rely on traffic diversion and alternate route capacity to manage congestion. System impacts were evaluated using a microscopic simulation model (VISSIM) to emulate traffic conditions on the I-95/I-395 corridor with and without ICM. The corridor included six to eight general purpose lanes, two reversible HOV lanes, a primary arterial (US-1), commuter rail services (Virginia Railway Express), Metrorail services (Franconia to Washington, D.C.), bus services, and park-and-ride facilities in Northern Virginia.
The following ICM applications and strategies were modeled.
- Variable speed limits (VSL) – VSL applications seek to improve dense traffic flow by varying speed limits across the length of the freeway to avoid traffic flow breakdown. The compliance rates modeled in this study ranged from 45 to 90 percent to evaluate a range of expected performance.
- Ramp metering - This application regulates traffic the flow at ramp meters to improve freeway traffic flow and safety during merging conditions. Metering rates between 500 and 900 vehicles/hour were modeled for 10 ramps in the study area.
- Transit signal priority (TSP) – The model used a constant extension period of 15 seconds to facilitate the operation of TSP.
- High occupancy toll (HOT)/high occupancy vehicle (HOV) lanes and HOV bypass – The model assumed prevalent traveler information would generate 0 to 15 percent more HOV users which would otherwise be SOV travelers.
- Increased transit and parking capacity -Taking into account the addition of 3000 new parking spots proposed within the corridor the research team assumed 7.5 to 23 percent of single occupancy vehicle (SOVs) trips would be attracted to transit.
- Financial incentives (reduction in fees for transit and parking) - The model assumed 0 to 7.5 percent of SOV travelers would choose transit as a result of incentives and new services offered.
Performance metrics measured with and without ICM included average vehicle flow, average travel times, average delays, and average emissions as agreed upon by corridor stakeholders. The authors noted that assumptions had to be made regarding traveler response to real-time/short term traveler information. For the analysis it was assumed that all the necessary means by which real-time traveler information could be disseminated were employed to inform drivers on the corridor.
A variety of ICM strategy combinations were tested during incident and non-incident conditions across a range of ICM parameters. The model was calibrated against existing conditions as a baseline and then incident conditions were emulated by stopping traffic on three of four general purpose lanes on I-95 north between the westbound off-ramp at SR-123 and westbound on-ramp at SR-123. Results excerpted from the source report are shown below.
Simulation results indicated a comprehensive ICM program that promotes mode shift to transit on the I-95/I-495 corridor (north) would increase person throughput by 38 percent and 14 percent during incident and non-incident conditions, respectfully; have little impact on HOV lanes; and reduce overall travel times on a parallel alternate route (US-1) by 29 percent.