Malcolm Wardlaw, DECEMBER 2002, TEC - 352 Cycling
Most bicycle journeys are quite short; one quarter is of less than a mile, while the mean distance is 2.4 miles. There will be some overlap of walking and cycling as options, so it is reasonable to compare on the basis of risk per kilometre. The standard unit is fatalities per billion kilometres (f/Bnkm).
It is also pertinent to compare the risks per hour, since for all three main modes the mean trip duration is in the range 15-20 minutes. Time-based exposure will thus indicate the mean trip risk. The standard unit is fatalities per million hours’ use (f/mhu). Some comment will also be made on risk of death per year.