Analysis of traffic on a two-lane road is approached in the first part of this paper by a microscopic deterministic model, traffic density being kept constant by means of a circular road. The results are transferred afterwards to a macroscopic stochastic system. Some of the data used in the deterministic model are looked upon, in the second part, as random observations from the macroscopic stochastic system. The average speed of a car having a given free speed and travelling on a road with a given density is obtained. Secondary results concerning average delay period and average free speed period are also derived.