Stability of Connected Vehicle Platoons with Delayed Acceleration Feedback

Wireless vehicle-to-vehicle communication technologies such as the dedicated short range communication (DSRC) may be used to assist drivers in sensing and responding to impalpable information such as the precise acceleration of vehicles ahead. In this paper, we investigate the impact of delayed acceleration feedback on traffic flow using a nonlinear car-following model. It is shown that acceleration feedback can improve the stability of uniform traffic flow, though excessive acceleration feedback leads to undesired high frequency oscillations. Additionally, time delays in the communication channel may shrink the stable domain by introducing mid-frequency oscillations. Finally, we show that one may stabilize vehicle platoons using delayed acceleration feedback even in cases when finite driver reaction time would destabilize the system. Our results may lead to more robust cruise control systems with increased driver comfort in connected vehicle environment. INTRODUCTION The analysis and control of transportation systems is in the interest of many research communities [1]. Ideas of traffic control using intelligent vehicles originated in the late 1930s, but were not widely considered until the 1990s [2]. In the last two decades, research in automotive control led to the development of radar-based autonomous cruise control (ACC) which can have a positive impact on vehicle safety, driver comfort, and highway efficiency [3]. Emerging wireless vehicle-to-vehicle communication technologies are expected to provide additional benefits for safety and mobility [4]. Data transmitted between vehicles may be incorporated in the ACC controller or can be used in ∗Address all correspondence to this author. driver assist systems even when the vehicle is not equipped with radar. Recently, large scale experiments validated the applicability of dedicated short range communication (DSRC) for vehicleto-vehicle (V2V) communication [5]. This technology, among many things, allows the transmission of acceleration signals along vehicle platoons that may be used to “predict” the motion of the vehicles ahead. While human drivers have access to a coarse version of this signal by monitoring the brake lights, knowing the precise value of acceleration may lead to significant improvements as has been demonstrated in other applications [6]. The precise acceleration information may be displayed to the driver or incorporated in cruise control algorithms of connected vehicles. However, DSRC devices transmit information intermittently, in every 100 ms, which may increase significantly when packets are dropped [4]. This introduces time-varying time delays into the control loops of communication-based ACC systems [7]. In this paper, we approximate time-varying delays with their average which has been used in the literature for semidiscretization of delay systems [8]. We evaluate the stability of the uniform flow using ring-road and platoon configurations, and show that the stability results are equivalent in both cases. Our results show that incorporating acceleration feedback is beneficial for stability, but the acceleration gain should be kept below certain thresholds. Moreover, increasing the communication delay leads to additional regions of instability with mid-frequency oscillations. Finally, we demonstrate that it is possible to stabilize vehicle platoons using acceleration feedback even in cases when human drivers (responding to the headway and relative velocity) cannot stabilize the flow due to their reaction time. 1 Copyright © 2013 by ASME Proceedings of the ASME 2013 Dynamic Systems and Control Conference DSCC2013 October 21-23, 2013, Palo Alto, California, USA