The primary goal of the research was to examine the system-wide impacts of early-deployment Cooperative Adaptive Cruise Control (CACC) dedicated lane strategies on roadway performance based on a variety of external factors such as overall demand, market penetration of the equipped vehicles, dedicated lane use strategy and CACC operational parameters such as inter-vehicle headway, critical gap for leading and following vehicles, and critical speed differential for leading and following vehicles.
CACC technology uses a combination of sensors and vehicle-to-vehicle and infrastructure-to-vehicle communications to enable vehicles to automatically adjust their speed to the speed of a preceding vehicles in the same lane. Dynamic Speed Harmonization (DSH) systems, typically controlled by management centers, dynamically adjust vehicle speeds in response to downstream congestion in an effort to improve throughput and reduce congestion shockwaves that can contribute to secondary crashes.
A simulation based approach was used to assess the operational and safety impacts of CACC and DSH at different levels of market penetration. The simulation test bed represented a 13-mile section of I-66 in Northern Virginia. The facility included one peak-hour peak-direction HOV 2+ lane, two to three general purpose lanes, and a shoulder lane made available during peak periods.
The simulation used a modified Intelligent Driver Model (IDM) enhanced with lane-change logic to assess the impacts of a CACC dedicated lane on traffic flow. DSH impacts were assessed using simulation software (VISSIM).
- Modeling results showed that with 10 percent CAV market penetration, dedicating a lane exclusively to CAVs will degrade freeway performance in terms of overall throughput. However, when market penetration reaches 25 percent, overall throughout will improve.
- Improvements of about two percent were observed for scenarios that combined CACC and DSH applications at 25 percent CAV market penetration.