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It Won't Kill You To Slow Down

There are a lot of misconceptions about the role that speed plays in crashes. Protect yourself and your loved ones by getting the facts.

It Won't Kill You To Slow Down

Road safety issues, including speeding, have been subjected to scientific analysis for nearly one hundred years and a vast body of research has been developed. The consensus in road safety  best practice is:

  • The faster you drive, the worse the crash will be if you get in one because of the greater force involved 
  • The faster you drive, the more likely you will be in a crash because you will have less time to react to unexpected hazards. 
  • Even small decreases in mean speed travelled equal many lives saved.

In a 2006 study, The Organisation for Economic Co-operation and Development (OECD) and the European Council of Transport Ministers determined that excessive or inappropriate speed was the full or partial cause in approximately one third (33%) of all fatal crashes. Put another way, SPEED KILLS.

Know the Difference

“Speeding” is driving above the speed limit whilst “excessive speed” is driving way above the speed limit, and you can be arrested for it. This applies at 30 km/h or more in an urban area and 40 km/h or more outside an urban area or on a freeway. Under Sections 35 and 36 of the National Road Traffic Act, 93 of 1996 your driver’s licence will be suspended if you are convicted of excessive speed.

“Inappropriate speed” is driving too fast for the conditions; for example, driving at the speed limit in heavy rain.

Why Speed Kills

 Speed has two main relationships with road safety

  1. The most direct link is aggravation of severity: greater collision speeds mean more force unleashed on the victims and thus speed directly influences the likelihood of death or serious injury. This is particularly so when vulnerable road users such as pedestrians, cyclists and motorcyclists are involved in a collision with another vehicle.
  2. The second relationship, a bit more complex, is the causal role of speed in a road trauma incident. The higher the speed at the point where a crash becomes likely, the less time there is for the driver to react, and the increased chances of skidding or other events influencing loss of control. So higher speeds play a very significant role in causing crashes.


Q: Is keeping to the speed limit safe?

A: Not always. South Africa has very high speed limits compared to countries with low road crash fatalities. In particular, the standard speed limit in urban areas is 60 km/h, which is very high for some areas, particularly where there are many schoolchildren and other pedestrians. In addition, speed limits are determined for good daytime conditions, and you should lower your speed in heavy traffic, at night or in bad weather, or any circumstance where visibility is reduced.

Q: Is driving slower than the rest of the traffic dangerous?

A: Scientists working in road safety in the 1950’s and 1960’s (e.g. Solomon, 1964) established a causal link between speed variation from the norm for a given road, and likelihood of a crash. It was long-believed this held true for both slower vehicles and faster vehicles, although more modern research (e.g. Kloeden et al, 1997; 2001; 2002) shows that the relationship is only significant for vehicles going faster than the mean.

These early findings, however, appear to have left a considerable impact, in that there are many people today who believe that relative speed is the most important consideration when selecting speed, an approach which is open to be manipulated to justify high travelling speeds.

Q: Are lower speed limits safer?

A: Yes. Lower speed limits have been shown to reduce road deaths and injuries considerably. Developed countries have adopted progressively lower speed limits in recent decades, in response to increased traffic volumes and large numbers of deaths, particularly among pedestrians and other vulnerable road users.

Q: Do lower speed limits make drivers more compliant with the speed limit?

A: No, they don’t necessarily have an effect on overall compliance, which is more responsive to law enforcement and behaviour change through education. But they do have an effect on the mean speed travelled, which is very important for crash rates. Small changes in mean speed travelled translate to significant reductions in fatal and serious crashes.

The Nilsson equation (Nilsson, 1982) is still used today to calculate fatalities reductions through speed limit reductions and has been shown to remain true through studies in a wide variety of jurisdictions and conditions. Nilsson’s model, for example, has been used to show that a 1 km/h reduction in mean speed travelled from 120 km/h to 119 km/h equals a fatalities reduction of 3.8%.

Q: Should South Africa lower its speed limits?

A: Transport specialists in South Africa are very divided on this issue, with a majority being opposed. However, those specialists opposed to speed limit reductions appear to be uninformed regarding international research confirming the success of speed limit reductions in bringing down death rates down around the world (Steunenberg, Sinclair, 2014).

The argument is also made that South Africa lacks the capacity to enforce the existing speed limits and should therefore not tamper with them, although high levels of law enforcement have not been proven to be an absolute prerequisite for success. This opposition to lower speed limits reflects broader society where resistance to lower speed limits is even more pronounced. There is also a high level of suspicion among the public regarding the motives of the authorities whenever speed limit reductions are considered.

This is an international trend and it can take many years of reduced road fatalities to convince the more sceptical of the value of lower speed limits. However, international research also largely suggests that speed limits must be credible to be respected, which is the key to compliance. This implies that a great deal of public education about speed and the role it plays in road safety is still required in South Africa before the public will be accepting of lower speed limits.