A Theoretical Model for Evaluating the Impact of Connected and Autonomous Vehicles on the Operational Performance of Turbo Roundabouts

This article presents a methodology to estimate the entry capacity (EC) and the total capacity (TC) of basic turbo roundabouts under partial and fully connected and automated vehicles (CAVs) environments. Entry capacity calculations are partially based on capacity models and adjustment factors proposed by the HCM 7th edition, taking into account different proportions of CAVs in traffic streams. The proposed methodology was applied to a case study concerning a basic turbo roundabout with different traffic demand and market penetration levels (MPLs) of CAVs. It was assumed a traffic stream consisting of 100% passenger cars with MPLs of CAVs from 0% to 100%. The research proves that with the increase in MPLs of CAVs, entry capacities increase accordingly and delays and queues decrease. To maximize the total capacity, a control area was also hypothesized where CAVs start to communicate with a turbo roundabout manager system. The system should be able to distribute and channel CAVs, and therefore the entering flows between entry lanes and find the values of the maneuver distribution factors (α, β, γ, δ) between the right lane and the left lane of entries to maximize the TC for each origin–destination matrix of traffic flows.