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The Real Risk

Road safety: Do more cars mean more accidents?

About the author

David Spiegelhalter is Winton Professor of the Public Understanding of Risk at the University of Cambridge, UK. His professional background is in medical statistics. He is a frequent contributor to the media, and has been an advisor on risk issues as diverse as breast implants, volcanic ash, clinical trials, surgical mortality, and the inquiry into mass murderer Harold Shipman. He is a Fellow of the Royal Society and was awarded an OBE in 2006. You can see more of David’s explorations of risk at the Understanding Uncertainty website, or follow him on Twitter at @undunc

Road safety

(Copyright: Thinkstock)

How crunching the numbers reveals some startling differences in the risk of road accidents between richer and poorer countries.

Karl Benz would likely be shocked at the continued popularity of his invention. Our appetite for cars has grown to a point where there is now around one car for every 11 people in the world. Reasonably, you may think that more cars means more road accidents. But, as ever, numbers tell a more complex truth.

Take the UK as an example. In 1950, a few years before I was born, there were 4.4 million vehicles registered in Britain, one for every 11 people. In 2010, there were 34 million vehicles, eight times as many, and more than one for every two people. There were 5,012 deaths on UK roads in 1950, but by 2010 the number of deaths had dropped by 63% to 1,850. When I remember how as a child I enjoyed riding in the front seat of our old van, which had no regular safety inspection or seat belts, and how people used to drive to the pub, drink all evening, and then meander home, I am not really surprised by these extraordinary changes. 

If we translate these figures into the chance in a million of dying, or micromorts, there was an average of 102 micromorts per person per year in 1950, dropping to just 31 micromorts per year in 2010. Or to put it another way, each 100,000 vehicles in 1950 were responsible for 114 deaths, but by 2010 they were responsible for only five deaths.

Crash test

Almost all of the richer nations have followed this pattern, despite traffic increasing. In the 30 years between 1980 and 2009, road fatalities fell by 55% in Australia, 69% in France, 63% in Britain, 54% in Italy and 58% in Spain. The reduction in the US was only 34%, while deaths slightly rose in Greece. For countries that collect the relevant data, we can get the average number of micromorts per 1,000 kilometres a vehicle travels: four in the UK, seven in the USA, 10 in Belgium, 20 in Korea, 40 in Romania and 56 in Brazil.

Counting accidents and injuries is more tricky – what exactly counts as an injury? But taking the UK as an example, its figures for being injured have hardly changed: in 1950 there were 167,000 accidents with 196,000 injuries; in 2010 there were 154,000 accidents with 207,000 injuries. People still crash into each other about 400 times a day, but the proportion of these accidents that are fatal has dropped staggeringly – thanks to speed limits, safety features, and improved and quicker medical care.

Sadly these trends are not observed the world over. While the average risk for an individual from dying on the roads in high-income countries is 103 micromorts per year, it is 205 in low- and middle-income countries. Of the estimated 3,500 people killed a day worldwide, 3,000 are in the developing world, in spite of those countries containing less than half of all cars on the road. Notable in the per-capita list is South Africa, which sees 15,000 road deaths each year, a statistic that was brought into sharp relief when Nelson Mandela’s great grand-daughter Zenani was killed

Smeed and speed

Who bears this risk again exposes a divide between richer and poorer nations. In richer countries, the majority of road fatalities are the occupants of cars. In poorer countries it is what are known as “vulnerable road users”: pedestrians, cyclists and whole families squeezed onto a single small motorbike. For instance, 70% of all road deaths in Thailand are riders of two-wheeled vehicles.

The World Health Organisation (WHO) points out that only 47% of countries have laws about safety features such as speeding, drinking, seatbelts, helmets and child restraints. And these are often not enforced. Not that this shows any sign of improving. The WHO also predicts that road traffic injuries will rise from its current ninth position in the cause-of-death league table to fifth place by 2030 – causing 2.4 million deaths, as well as between 20 and 50 million injuries, largely of young people, and at enormous cost to the economies.

It might seem odd that countries with fewer cars are riskier places for road travel, but “Smeed’s law” of traffic says that deaths per vehicle decline strongly as roads get busier – it is empty roads that are so lethal. This is reflected in some extraordinary statistics about Ethiopia: the WHO report states its 244,000 registered vehicles in 2007 managed to kill 2,517 people, the majority of which were pedestrians. That is one death per year for every 100 vehicles. If the US had the same rate with its 250 million vehicles, this would mean 2.5 million deaths on the roads each year – 75 times the current amount of around 32,000 deaths.  

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