Traffic Dynamics: Studies in Car Following

TLDR

Vehicle following dynamics on highways and the propagation of disturbances along a line of cars have been studied. The study theoretically analyzes various car‑following laws. Experimental and theoretical results show that car acceleration depends on the velocity difference with a 1.5‑s lag and a 0.37 s⁻¹ proportionality constant, and that traffic flow becomes unstable when the lag‑constant product exceeds 0.5, indicating drivers operate near instability.

Abstract

The manner in which vehicles follow each other on a highway (without passing) and the propagation disturbances down a line of vehicles has been investigated. Experimental data is presented which indicates that the acceleration at time t of a car which is attempting to follow a leader is proportional to the difference in velocity of the two cars at a time (t − Δ), Δ being about 1.5 sec and the proportionality constant being about 0.37 sec −1 . It is shown theoretically that the motion of a long line of vehicles becomes unstable when the product of the lag time and the proportionality constant exceeds one-half. The experimental data implies that driving is done on the verge of instability. A variety of other laws of following is analyzed theoretically.