  Understanding the mechanisms responsible for the emergence and evolution of
oscillations in traffic flow has been subject to intensive research by the
traffic flow theory community. In our previous work, we proposed a new
mechanism to explain the generation of traffic oscillations: traffic
instability caused by the competition between speed adaptation and the
cumulative effect of stochastic factors. In this paper, by conducting a closer
examination of car following data obtained in a 25-car platoon experiment, we
discovered that the speed difference plays a more important role on
car-following dynamics than the spacing, and when its amplitude is small, the
growth of oscillations is mainly determined by the stochastic factors that
follow the mean reversion process; when its amplitude increases, the growth of
the oscillations is determined by the competition between the stochastic
factors and the speed difference. An explanation is then provided, based on the
above findings, to why the speed variance in the oscillatory traffic grows in a
concave way along the platoon. Finally, we proposed a mode-switching stochastic
car-following model that incorporates the speed adaptation and spacing
indifference behaviors of drivers, which captures the observed characteristics
of oscillation and discharge rate. Sensitivity analysis shows that reaction
delay only has slight effect but indifference region boundary has significant
on oscillation growth rate and discharge rate.
