Abstract
The interaction between the speeds of cars following each other mainly depends on the gaps between the vehicles, and for each car it is dominated by the speed of the immediately preceding vehicle. This is the basis of a Markov model for the gaps and speeds. In passing, distributions for gaps and speeds are derived. A generalised gamma distribution allows translation of the main feature of the gamma distribution without changing the support of the distribution on the entire positive axis. A good fit to the speed data is given by this distribution. (A)