A comparison study on the growth pattern of traffic oscillations in car-following experiments

TL;DR

This study compares traffic oscillation growth patterns in two car-following experiments, revealing consistent concave growth of speed standard deviation and insights into traffic flow dynamics and experimental design.

Contribution

It demonstrates that traffic oscillations grow concavely in different experimental setups and compares circular and straight track experiments, informing future traffic flow research.

Findings

Speed standard deviation grows concavely in both experiments

No significant difference between datasets in oscillation growth patterns

Drivers following closely increase acceleration standard deviation

Abstract

The evolution of oscillations is a very important issue in traffic flow studies. A recent car-following experiment (Experiment-I) showed that the speed standard deviation grows in a concave way along a platoon of vehicles following one another. This finding indicates that the traditional traffic instability mechanism is debatable, in which the speed standard deviation initially grows in a convex way. This paper has investigated the growth pattern of traffic oscillations in another car-following experiment (Experiment-II) and compared it with that in Experiment-I. It is shown that the speed standard deviation also exhibits concave growth characteristics in Experiment-II. The paired-sample t-test and the Mann-Kendall (MK) trend test showed that there is no significant difference between the two datasets. However, the acceleration standard deviation was remarkably larger in Experiment-II since drivers were asked to follow closely. Furthermore, a comparison experiment has been performed which indicates that the set of experiments on a circular track can be considered equivalent to that on a straight track. Our study is expected to shed light not only on traffic flow dynamics itself but also on the future design of the experiment scheme.