AbstractIn this paper the author formulates and derives a discrete traffic counting distribution and a passing rule which lead to bunches of zero or one“fast”vehicle behind a“slow”vehicle.“Slow”vehicles are distributed in a Poisson fashion and, except for those instants at which passing occurs, the constrained or“fast”vehicles follow immediately behind a“slow”one. The counting distribution is a simple example of one in which successive inter-vehicle spacings have the Markov property.