When breath-alcohol testing is done for evidential purposes, an observation period after arrest of 15–20 min is necessary before results are considered valid for prosecution [28]. This waiting time is necessary to avoid problems caused by any alcohol remaining in the mouth and/or oral mucosa after the last drink [29]. In the present study, there was no 15 min observation period before making the roadside breath alcohol test, which means that some of the abnormally high breath-test results can be explained by contamination from mouth-alcohol and a recent drink.