One of the most inflammatory and divisive topics in road or highway safety is that of speed in relation to safety.

The first question that has to be addressed is what exactly do we mean in this context by the word “speed”?  It is very important not to fall into the trap of thinking it only relates to breaking the posted speed limits, even though that is still a serious issue (see below).

A panned photo of a car travelling at speed on a leafy rural road.
Breaking the posted speed limit often contributes to serious or fatal crashes.  However, if there are problems on the road, then it is easy to do a potentially dangerous speed even within the posted limit. This is called driving at an inappropriate speed for the circumstances, and it is particularly common — and deadly — on rural roads. (Copyright image.)


The Traffic Injury Research Foundation [TIRF], Canada, in their annual Road Safety Monitor, states that speeding is driving any amount over the posted speed limit or driving too fast for conditions, and this definition or something extremely similar seems to be used around the developed world.


What Can Happen When You Cut Your Speed by Just 3mph (5km/h)?

Many people were sceptical that driving 5 km/h slower could make a difference to speed on impact. (Video from Transport Accident Commission, Victoria)

The speeds given in the above video in kilometers per hour (km/h) can be converted to mph as follows:

  • 65 km/h = 40mph
  • 60 km/h = 37mph
  • 32 km/h = 20mph
  • . 5 km/h = .. 3mph

To understand what might seem like a crazy result in the Australian video, above, it is necessary to know the effect that extra speed has on the distance it takes to stop a vehicle.  Put simply, if a driver were to double his or her speed — from, say, 20-40mph or 30-60mph, it would not take twice the distance to stop when braking hard, as most people would expect, it will take approximately four-times as far.  This outcome is a law of physics that cannot be escaped.  Anyway, the result is that even small increases in speed do significantly extend the distance it takes to stop — as shown in the video — so if a collision occurs, it will happen at a significantly greater speed and will be much more likely to cause injuries or even death.

The same overall subject was covered in an older but still incredibly worthwhile video from Britain, originally released in the 1990s but re-released by the Think! campaign in 2007.

This video shows that another common argument that crashes are only caused by people doing “inappropriate” speeds, as opposed to simply breaking the posted speed limits, is actually a nonsense.



Once again this illustrates the extra stopping distance needed to stop, in this case by increasing the speed from just 30mph to 35mph.

In doing so, it uncovers a massive and undeniably deadly common practice.  Most people are told, either by their dad or their friends that in many places they will “get away with speeding” in towns and cities as long as they don’t go more than  about 5mph over the limit, “because the police won’t do anything.”   But as this video shows:  That’s not the point!

Another sad fact is that, quite frankly, police officers are by no means always the best judge in this context.  Don’t get me wrong;  I’m not slamming police officers — I was one myself!  But while police officers get a lot of training in the law and how to do their job correctly, they typically learn nothing at all about the research-based side of traffic safety, to guide their actions towards the best possible results — meaning the greatest reductions in casualties.  As a result, I have heard many police officers, on both sides of the Atlantic, voicing the ill-informed opinion that going just a few miles an hour over an urban speed limit does not cause crashes.  Sadly, however, this — as stated above — is simply not correct, and hospital or mortuary lists prove this point tragically well.

In my own case, I was not only a highly-specialised and highly trained traffic patrol police officer, qualified as a UK “police advanced driver and motorcyclist,” which are the highest road driving qualifications in the world,  I was also my force’s first active, hand-held radar instructor, and a specialist in working with teenage and early-20s drivers and riders on staying safe.  But since I got into reviewing and working with driver safety research, almost 20 years ago, I have learned countless things that I wish I had known in proper and significant detail as a police officer.  That’s still not a criticism.  The fact is that in Britain we had significant amounts of traffic-related training in the police, but training is very expensive and whether we like it or not there has to be a limit.

I will close this article with two simple but irrefutable statements:

  1. If a driver is speeding — by any definition of that word — s/he will have less time to respond to something that happens up ahead, and this equates to less distance in which to stop (see the 2nd video).  If a collision occurs, it will involve dramatically greater forces (see video 1) and will therefore be more likely to cause serious injuries rather than minor ones, or in the worst cases more likely to cause deaths rather than injuries.
  2. In 2016 (the latest year for which official figures have yet been published) an outrageous 5,987 pedestrians alone were killed on America’s roads, and tens of thousands more were badly injured. Now add the bicyclists. Now add other road users.  The fact is that many of these casualties were directly due to drivers who were using too much speed, whether those speeding individuals want to believe it or conveniently deny it.
Written by Eddie Wren
March 13, 2018
(c) Advanced Drivers of North America

Speed… Is it Really a Major Safety Issue or Do the ‘Experts’ Exaggerate?

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