Modeling Study on Connected and Fully Automated Vehicle Platoons Estimated up to 31 Percent Capacity Increase at 50 Percent Penetration.
Research Study Modeling Platooning of Connected Fully Automated Vehicles for a Sample Freeway Segment Considering Conservative and Uncoordinated Platooning Behaviors.
Capacity of a freeway lane with platoons of autonomous vehicles mixed with regular traffic
Summary Information
Connected Automated Vehicles (CAV) traveling in platoons at very short time gaps could be a viable traffic demand management strategy. This study provided a generalized macroscopic model to estimate the average CAV platoon length for a given traffic demand and penetration rate of CAVs that would achieve capacity improvement. Two different platooning schemes, cooperative and opportunistic (i.e., uncoordinated), were compared and represented the best- and worst-case scenarios, respectively. The proposed model was applied to stationary free-flowing traffic at equilibrium on a sample freeway segment.
METHODOLOGY
This study implemented specific car-following models for platoons of regular vehicles and CAVs and assessed the resulting capacity of the mixed traffic freeway lane for different traffic demands and market penetration rates for CAVs. Opportunistic platooning was defined as when CAVs formed a platoon by chance and cooperative platooning was defined as where lane management strategies were used to form platoons of CAVs and forced out RVs out of the platoon lane. Under the cooperative platooning scheme, it was assumed that if the platoon length was not limited, all CAVs within the platooning range would create a single platoon. The effects of a maximum platooning distance resulting from the communications range of on-board equipment were considered, which allowed regular vehicles to occupy the empty lane space generated by the shorter space gaps between CAV's in the platoon. Two parameters, namely (i) latency of vehicle-to-vehicle communications and (ii) acceptable relative difference in the CAV’s maximum deceleration, were used to define “optimistic” and “conservative” scenarios, respectively.
FINDINGS
- The results showed an estimated 31 percent capacity increase at 50 percent penetration of CAVs with cooperative driving, under conservative conditions.
- The results also showed an estimated 14 percent capacity increase at 50 percent penetration of CAVs with opportunistic driving, under conservative conditions.
- Under optimistic conditions, the corresponding values for capacity increase were 49 percent for cooperative driving, and 21 percent for opportunistic driving.
