Archival statistics show marked negative correlation between the annual traffic accident rate per unit distance driven in a jurisdiction on the one hand and the same-year amount of mobility (units of distance driven per head of population) on the other. From 1923 to 1996, the death rate per 100 million miles driven in the U.S. fell on average by between 3% and 4% per annum. In the same period, the mileage per head of population rose on average by between 3% and 4% per annum. The product between these two rates (Acc/Km multiplied by Km/Capita), i.e., the death rate per head of population (Acc/Cap), showed no clear upward or downward trend over the period in question; it was about the same in 1996 as it had been 73 years earlier, in 1923. Major fluctuations in the annual fatal Acc/Cap rate did, however, occur in this three-quarter century and these fluctuations appear to be largely due to variations in the business cycle. Data from several other countries support this notion. We infer from these observations that interventions that allow drivers to increase their moving speeds-while maintaining both their accident rate per unit time of exposure to risk, and their travel time budget-have an enhancing effect on mobility. These interventions include seatbelts, airbags, wide and forgiving roads, collapsible steering columns and otherwise more crashworthy cars. Conversely, the creation of road conditions, such as "traffic calming" devices (e.g., speed bumps, traffic throttles and chicanes), that compel drivers to slow down, can be expected to decrease mobility while essentially having no effect of the accident rate per capita per year. By the same logic, however, the accident rate per unit distance driven would be expected to rise again. We, therefore, propose that these devices are counterproductive to safety, although they may well have beneficial effects in other respects. (Author/publisher)
Abstract