From 1980 to 1982, two investigations of the chronic pollution of roadway runoff water were carried out in areas having different pluviometric characteristics. The runoff from two hundred pluviometric events was characterized using highly rigorous methodologies, with a view to estimating the annual pollution load.
The annual loads were determined; they show that the official instructions hither-to followed were rather pessimistic. On the other hand, greater vigilance is required as regards the loads that may be contributed by an isolated event, but it is not possible to characterize the parameters that will give rise to such an event. A few rain events can introduce into the environment, in a short time, as much as 30% of the annual pollution load of motorway runoff waters.