Protected Turning Movements of Noncooperative Automated Vehicles: Geometrics, Trajectories, and Saturation Flow

Abstract

This study is the first to quantify throughput (saturation flow) of noncooperative automated vehicles when performing turning maneuvers, which are critical bottlenecks in arterial road networks. We first develop a constrained optimization problem based on AVs' kinematic behavior during a protected signal phase which considers both ABS-enabled and wheels-locked braking, as well as avoiding encroaching into oncoming traffic or past the edge-of-receiving-lane. We analyze noncooperative ("defensive") behavior, in keeping with the Assured Clear Distance Ahead legal standard to which human drivers are held and AVs will likely also be for the foreseeable future. We demonstrate that, under plausible behavioral parameters, AVs appear likely to have positive impacts on throughput of turning traffic streams at intersections, in the range of +0.2% (under the most conservative circumstances) to +43% for a typical turning maneuver. We demonstrate that the primary mechanism of impact of turning radius is its effect on speed, which is likely to be constrained by passenger comfort. We show heterogeneous per-lane throughput in the case of "double turn lanes." Finally, we demonstrate limited sensitivity to crash-risk criterion, with a 4% difference arising from a change from 1 in 10,000 to 1 in 100,000,000. The paper concludes with a brief discussion of policy implications and future research needs.

Understanding the Determinants of Lane Inefficiency at Fully Actuated Intersections: An Empirical Analysis

“…Figure 2 displays the instant discharge flow rates of vehicles during two observed green periods (G 1 = 36 s and G 2 = 38 s), both characterized by an identical saturation flow rate of 0.480 veh/s/lane (1728 veh/h/lane) and a consistent number of queued vehicles, which, in this case, is 11. Note that apart from the studies in the literature that provide saturation flow rate values in pcu/h/lane [44][45][46][47], there are also those presenting these values as vehicle/h/lane [38,48,49]. Therefore, in this study, the saturation flow rate was calculated as vehicles per hour per lane using the time headways of the vehicles.…”

New Approach to Estimating the Saturation Flow Rate of a Shared Lane with Permitted Left Turns

“…A model for determining the saturated flow of exit lanes for left-turn intersections can be seen in paper [16]. The saturation flow rate analysis under the automated vehicle environment can be found in paper [17].…”