Intelligent cruise control systems and traffic flow stability

✍ Scribed by Swaroop Darbha; K.R. Rajagopal

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 918 KB
• Volume: 7
• Category: Article
• ISSN: 0968-090X
• DOI: 10.1016/s0968-090x(99)00024-8

✦ Synopsis

There are two kinds of stability associated with trac ¯ow problems ± string stability (or car-following stability) and trac ¯ow stability. We provide a clear distinction between trac ¯ow stability and string stability, and such a distinction has not been recognized in the literature, thus far. String stability is stability with respect to intervehicular spacing; intuitively, it ensures the knowledge of the position and velocity of every vehicle in the trac, within reasonable bounds of error, from the knowledge of the position and velocity of a vehicle in the trac. String stability is analyzed without adding vehicles to or removing vehicles from the trac. On the other hand, trac ¯ow stability deals with the evolution of trac velocity and density in response to the addition and/or removal of vehicles from the ¯ow. Trac ¯ow stability can be guaranteed only if the velocity and density solutions of the coupled set of equations is stable, i.e., only if stability with respect to automatic vehicle following and stability with respect to density evolution is guaranteed. Therefore, the ¯ow stability and critical capacity of any section of a highway is dependent not only on the vehicle following control laws and the information used in their synthesis, but also on the spacing policy employed by the control system. Such a dependence has practical consequences in the choice of a spacing policy for adaptive cruise control laws and on the stability of the trac ¯ow consisting of vehicles equipped with adaptive cruise control features on the existing and future highways. This critical dependence is the subject of investigation here.