Theme II. Speed limits and the driver. The experience of the United States with the 55 mph speed limit.

There are 3 reasons why speed influences safety: (1) at higher speed, a vehicle travels further during driver reaction time; (2) braking distance increases with speed; (3) crash severity increases disproportionately with speed at impact. The author briefly reviews speed limits and safety in a number of countries, including the USA and examines the problems associated with the enforcement of speed limits (effectiveness of sanctions, citations and enforcement crackdowns). Public opinion polls in the US show a high level of public support for the 55 mph speed limit.