Smeed's law

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Smeed's Law, after RJ Smeed who first proposed the relationship in 1949, is an empirical rule relating traffic fatalities to motor vehicle registrations and population. Thus annually increasing traffic volume leads to a decrease in accidents per vehicle. It was posited after an analysis of figures from a number of countries over several decades.

Smeed's formula is expressed as:

[D = .0003(np^2)^]

or, weighted per capita

[ = 300* }]

where D is annual road deaths, n is number of registered vehicles and p is population.

Smeed showed this relationship worked with 20 different countries. The relationship was revisited by John Adams in 1987 who held that it was valid for a variety of countries over time, for example in Great Britain from 1909 to 1973. In 1995 Adams further showed the relationship worked for the data of 62 countries. However, the validity of Smeed's Law has also been disputed by several other authors (for example Andreassen 1985, Broughton 1988, Oppe 1991, Ammen & Naji 2000).

References

Smeed 1949. Some statistical aspects of road safety research. Royal Statistical Society, Journal (A) CXII (Part I, series 4). 1-24.

Adams 1987. [Smeeds Law: some further thoughts.] Traffic Engineering and Control (Feb) 70-73.

Adams 1995. Risk. London, UCL Press

Andreassen D. Linking deaths with vehicles and population. Traffic Engineering and Control, November 1985.

Broughton, J. Predictive models of road accident fatalities. Traffic Engineering + Control, May 1988.

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