Smeed’s Law Explained

The infamous Smeed’s law was coined by R.J. Smeed who proposed a relationship between empirical rule relating traffic facilities, traffic congestion and the country population.

The law establishes that increasing traffic volume (an increase in motor vehicle registrations) further leads to an increase in fatalities per capita, but a decrease in fatalities per vehicle.In laymen language, as motor vehicle ownership increases, death rates per vehicle decrease. The principal claims of the credit for this decrease are considered: safer vehicles, safer roads and safer road users.

Along with that, Smeed predicted that the average speed of traffic in central London would always be nine miles per hour, because that is the minimum speed that people can handle. He further predicted that any intervention intended to speed traffic would only lead to more people driving at this “tolerable” speed unless there were any other disincentives against doing so.

He further assessed that smart use of traffic lights might increase the number of cars on the roads but will not increase their speed. As soon as the traffic flows faster, more drivers would come to slow it down.

Smeed demonstrated his law as a law of human nature. He claimed that the number of deaths is determined mainly by psychological factors that are independent of material circumstances. People will drive recklessly until the number of deaths reaches the maximum they can tolerate. When the number exceeds that limit, they drive more carefully. Smeed’s Law merely defines the number of deaths that we find psychologically tolerable.

Smeed gave a formula to calculate the per vehicle fatality rate. The formula used is appropriate to describe the phenomenon that with low motorization the number of fatalities is increasing. Once reaching a certain threshold, the society will devote and can afford more efforts to turn the previous trends in road safety. The formula can be used both for cross sectional data of a given year to describe difference between countries and for time series of given countries

The ‘clockwise rotation’ of the Smeed’s relationship, suggested a higher fatality rate for a given level of vehicle ownership. The law also suggests that safer vehicles cannot be given any credit for the decrease in death rates over time.

Regional Specificity:

Some countries in the lower motorization phase have low fatality numbers but these figures have steadily been increasing in the last decade for e.g. China, Myanmar, and Philippines. Some others like Malaysia and Thailand suffer from much higher fatality rates but these rates are decreasing, especially in Thailand. The low Japan fatality rates show a further decrease.

The range of fatality figures between countries for a given car ownership level is quite large. These differences underline the fact, that the trends found are not like laws of nature. A country will not automatically follow the trend, but a lot has to be done to follow it; it is a result of many efforts in vehicle design, infrastructure safety, enforcement and education.

Road Safety:

According to Smeed’s research, the Asian countries show a quite embedded in terms of fatality rates and their trends. Many of them are in a declining road safety situation, where an increasing fatality rate per population due to growing traffic volume dominates, and there is not enough social attention to road safety.


His hypothesis in the field of road traffic safety has been criticized by several authors, who claim that fatalities per person have decreased in many countries, when the “Law” requires that they should increase as long as the number of vehicles per person continues to rise.


There is still a lot of scope for a long-lasting improvement, if the pace of economic and technological development as well as the change in social attitude is higher than the growth in traffic volume.