Variable speed limit control at fixed freeway bottlenecks using connected vehicles

Abstract

The connected vehicle (CV) technology is applied to develop VSL strategies to improve bottleneck discharge rates and reduce system delays. Three VSL control strategies are developed with different levels of complexity and capabilities to enhance traffic stability using: (i) only one CV (per lane) (Strategy 1), (ii) one CV (per lane) coupled with variable message signs (Strategy 2), and (iii) multiple CVs (Strategy 3). We further develop adaptive schemes for the three strategies to remedy potential control failures in real time. These strategies are designed to accommodate different queue detection schemes (by CVs or different sensors) and CV penetration rates. Finally, probability of control failure is formulated for each strategy based on the stochastic features of traffic instability to develop a general framework to (i) estimate expected delay savings, (ii) assess the stability of different VSL control strategies, and (iii) determine optimal control speeds under uncertainty. Compared to VMS-only strategies, the CVbased strategies can effectively impose dynamic control over continuous time and space, enabling (i) faster queue clearance around a bottleneck, (ii) less restrictive control with higher control speed (thus smoother transition), and (iii) simpler control via only one or a small number of CVs.

Theoretical conditions for restricting secondary jams in jam-absorption driving scenarios

“…Although we have used a single absorbing vehicle in this paper, several studies used active maneuvers of more vehicles for removing or mitigating traffic jams [26,31]. Analysis of string stabilities in JAD scenarios with multiple absorbing vehicles will contribute the further development of JAD, and warrants future work.…”

“…Based on the basic scenario of Ref. [26], we focus on a single-lane system with a bottleneck, as shown in the macroscopic view on a time-space diagram (Fig. 11).…”

“…Contrary to the scenarios of wide moving jams, vehicle 1 does not produce its initial perturbation. Instead of vehicle 1, this bottleneck triggers off traffic breakdown (a drop of flow rates) and causes a traffic jam [26,36]. The jam arises from O (0, 0) and its downstream head is fixed at this bottleneck (that is, v R = 0).…”

“…The absorbing vehicle goes from point A to B at the macroscopic absorbing velocity v a,bn,mac for dissolving the jam [26]. We obtain v a,bn,mac by substituting v R = 0 for condition (23):…”

“…This strategy is based on the fact that a traffic jam shrinks by restricting and enhancing the flow rate upstream and downstream of the jam, respectively. This strategy uses the first technologies (such as VSL and RM) [21,22], the second technologies (such as connected vehicles (CVs)) [25], and the combinations of both technologies [24,26]. Note that combinations of the first and the second strategies have also been investigated.…”