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

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.

Author: EddieWren

Eddie Wren is the CEO and Chief Instructor at Advanced Drivers of North America. His driver safety background is given at: http://www.advanceddrivers.com/ceochief-instructors-resumecvbio/

19 thoughts on “Speed… Is it Really a Major Safety Issue or Do the ‘Experts’ Exaggerate?”

  1. Hi Eddie,
    As always, your articles are a refreshing cool drink in the middle of a hot day.
    You are probably aware that the setting of speed limits in most US municipalities are largely based on the Solomon curve. (https://en.wikipedia.org/wiki/Solomon_curve). There is a lot of misuse of data from Solomon’s original study, and subsequent studies. The resulting actions after a ‘speed study’, more often than not, result in speed limits being raised not lowered. Solomon’s study showed that on a road with a given speed limit, that more collisions would involve the lower 15% cohort than the highest 15% of drivers, thus after a speed study, the limit will typically be set at the speed traveled by the 85th percentile.
    This seems to me to be asinine, as no consideration is given to other road users (e.g. pedestrians) or different classes of motor vehicle.
    Traveling at the speed limit will generally draw the ire of other motorists, which is quite challenging sometimes, as one will generally have to pull to the side to let the ‘better’ drivers pass. My anecdotal evidence is that driving at the speed limit on my regular journey in California I am in the slowest 2% of drivers. I take this sample over a 45 mile stretch of freeway early in the morning, and generally count 50 or so vehicles passing me for every one I pass. Which, put another, way implies a 98% non compliance with the posted speed limit.
    If I ask colleagues how much distance it takes to stop a vehicle from 70 mph, (or any other speed) they are all clueless! They however, generally agree it is anomalous to make the decision to decide to drive at some chosen speed above the speed limit, and yet remain oblivious to the requirements of stopping their vehicle.
    This ignorance is at the root of inadequate following distances, and makes it very difficult to meet your ‘prime directive’ of all drivers.. i.e. the ability to stop the vehicle, safely, within the distance seen to be clear etc.

    1. Indeed, John. The use of the 85th percentile is a fatally-flawed approach for the very reason you mention; the speeds are being decided by an entirely uninformed driving populace who pay little or no regard to adjacent or nearby factors which are critical in terms of the choice of speed. Town sports fields where a lot of young people play during vacations and evenings but which are not in a school zone are just one example.

  2. Very well articulated Eddie. What you have written is not any rocket science, but pure simple common sense, logic and a bit of physics. In spite of knowing a lot of this, people most often speed under all circumstances. As someone who has been driving for more than 35 years now, I just cannot fathom why people just blindly press the foot pedal the moment they see an open stretch of road. With road complexities increasing with each day, so many things could go wrong any instant and our human reflexes are just not built to handle that. As one road safety slogan goes, “People do not know the consequences of speed”. And they never do. Perhaps because in speed related crashes, the first one, being fatal, is almost always the last one too. The videos in the article as well as some “Wipe off 5” reconstruction videos of TAC cannot get more lucid in conveying the message. Still, one actual crash survival experience can be much more effective than anything else. Wish today’s technology could get us some real life simulated crash survival experience.

  3. It is unfortunate that, in the US, speed limits are set at the 85th percentile (e.g., the speed at which 85% of the vehicles travel at any given time. While that might be effective for major highways, it shouldn’t be used for town and neighborhood roadways, where speeding IACP typical, even in the presence of pedestrians, cyclists, driveway after driveway, etc. Unfortunately, many of these roads are designed for speed—straight, wide lanes, no speed calming measures like trees/shrubs, etc.

    1. Indeed, Robin. In my opinion, the commonplace reliance on the “85th percentile” for setting speed limits for regular, non-highway roads in the USA is extremely misguided because it relies entirely on — in this context — seriously under-informed and inadequately trained drivers to assess *all* relevant risk factors on each section of road and adjust their speed accordingly. For that approach to be effective, very observant drivers who also had significant risk-factor cognisance would be needed.

      I strongly agree with you about the need for speed calming measures, too.

      Thanks for your comments. They’re always welcome and helpful.

  4. In science, there is no such thing as speed. It’s called velocity, just as “warm” is not an accurate description either. Speed as compared to what? The sign, the traffic around you? Why is 5kph lower better than a 10kph reduction? Actually, 10kph might be too fast for some extreme conditions. Any vehicle at any velocity is “speeding” by some definition. I have a 1988 Mazda B2200 that I feel is “speeding” at the 120KPH speed limit, but my wife’s 2012 Mitsubishi is just getting comfortable. Speed limits were set during the 1970’s to reduce fuel consumption, and while faster speeds do indeed lead to greater injury, statistically, controlled access HIGHWAYS, where the posted speeds are higher, are safer than surface roads. Now we have an arbitrary 40kph over the posted sign is take your car away for a week, and the police DO leave you standing on the side of the road in BC minus your car. This is all in the name of “safety”. I think it stopped being about safety a long time ago. It’s now a big money pot for a government and ICBC who is addicted to the money. When police became pro active for traffic fines, I believe they lost the public confidence. IE, no matter how safely I’m driving, why don’t I feel safer with a police car following me?

    1. Thanks for your comments, Randy. However, as the original post was not written for scientists, but instead for ordinary drivers, I don’t think we need get too concerned about the difference between the words ‘speed’ and ‘velocity’.

      Similarly, I’m not sure what point you are making about the differences between a 5kph cut in speed by comparison with a 10kph reduction. I think — or at least I hope — that the message is straightforward, namely: cutting your speed significantly reduces your crash and injury risks.

      Also, given that you describe your wife’s Mitsubishi as “just getting comfortable” at 120 km/h (75mph), I think we had better not ask any questions about the speed at which it gets really comfortable! 😀

      Speed limits may indeed have been reduced during the 1970s but it would certainly appear that all divided highway speed limits and presumably at least the majority of other relevant speed limits in North America were subsequently raised again. Crash and casualty figures certainly went up again as this took place (although some people like to pretend that was not the case).

      My final point is that when you write “statistically, controlled access HIGHWAYS, where the posted speeds are higher, are safer than surface roads,” are you implying that the speed aspect somehow contradicts the higher levels of safety? If so, it is important to note that the additional safety comes from other factors such as very few intersections (which in any event use on- and off-ramps not sharper turns), all the traffic going one way, oncoming traffic separated by median guardrails, very straight roads, no roadside ‘furniture’, usually the presence of shoulders and plenty of run-off area, etc.

    2. Hi Randy

      In Science there is both speed and velocity.. Warning I’m going to get scientific here. Speed is a scalar value of distance divided by time. Velocity is a vector, which means it has both magnitude and direction. Acceleration (in physics) is defined as the rate of change of velocity, thus a force can be perceived even though the speed is constant but the direction changes (e.g. cornering). When a vehicle travels in a straight line at a constant speed and then travels along a curve, the speed is constant, but the velocity is not, because the direction changed. This distinction is very important in understanding and avoiding a skid.

    3. So are you actually defending driving 25+ over the posted limit?

      And no, speed limits were not set in the 70s. Interstate limits were lowered to 55 in the interest of saving gas as a result of the oil embargo. Virtually all of them have increased, many substantially since then, with the exception of urban interstate segments.

  5. Regarding your conclusion #1–no matter how fast a vehicle is traveling, the driver will still have the same TIME to observe/perceive/react to a hazard under most driving circumstances. However, the distance covered in a given distance varies linearly with speed, and the skid-to-stop distance is a squared function of speed, all other factors being equal.
    It has always been my opinion that speed (whatever the speed is, not necessarily speed above a posted speed limit) is caused by THE DRIVER. Guns don’t kill people; people kill people. Speed doesn’t CAUSE accidents, but higher speeds cause a reduction in a driver’s ability to stop for or otherwise avoid a hazard, and higher speeds cause higher impact energy when there is a collision. Pedestrians can be killed by a 25 mph impact by a vehicle being driven at 25 mph–I have investigated several such cases where I have been able to prove that the striking vehicle was actually traveling at or below the posted 25 mph speed limit but the struck pedestrian died. Should we, therefore, only drive at 10 or 15 mph, because someone might run out in front of us under circumstances which we can’t anticipate or avoid? I think not.
    If excessive speed is a causative factor in a collision, then the excessive speed is a driver error, in my opinion. Cars don’t kill people–people kill people.
    I have investigated all kinds of motor-vehicle crashes for over 46 years. Speaking of speed, a major complaint I have against law enforcement people is that they always charge someone who is crossing the path of an oncoming vehicle with failure to yield the right of way. I have seen a number of cases in which the oncoming vehicle was traveling over 85 mph in a 45 mph zone and over 100 mph in a 55 mph zone and, you guessed it, the officer charged the OTHER driver with failure to yield. Yet, when that other driver looked before pulling out, the speeding vehicle was so far away that there should have been plenty of time for the crossing vehicle to clear. When a driver sees an oncoming vehicle 300 feet away in a 45 mph zone, for instance, it would take a vehicle traveling 45 mph 4.5 seconds to close that distance, which is enough time for a crossing vehicle to turn left or cross without danger of a crash and with time to spare. At twice the posted speed limit, however, that time decreases to 2.25 seconds, which is enough time to get hit broadside by that oncoming vehicle. Failure to yield? Phooey! And the ridiculous speeds didn’t cause the crashes–it was idiot drivers, most of whom died essentially at the point of impact by driving at speeds way above anything rational or reasonable.
    My US$0.02

    1. Thanks for your comment, Ralph. I haven’t enough time to address all your points at present, but at this stage — in response to your own first paragraph — let me just mention that in what you call my “conclusion #1” I was not referring to perception/reaction time. I would have written that had it been the case. My use of the word “respond” was/is intended to denote the actions required to achieve the overall act of stopping, including the braking. I am very aware that reaction time is likely to be the same whatever the speed, and likely in the range of 1.33 to 1.5 seconds, depending on which research one nails one’s flag to. But as you confirm, at higher speeds this certainly does leave less time and distance in which to stop the vehicle.

      1. There is one other notable consideration in all of this. As speed increases the driver’s cone of vision typically narrows. Thus, there is often a reduction in what the driver actively sees and perceives.

  6. Great points – thanks Eddie.
    Last year I helped to organise a seminar on speed assist systems in London. See the report here:
    It includes the results of a pilot study by the University of Adelaide that analysed electronic data recorder data from hundreds of crashes in the USA (mostly NASS). From these actual crash data they reconstructed the crash and identified key vehicles that were speeding. They then re-ran the crash at the posted speed limit. One third of injury crashes would have been prevented and 22% of crashes would have been avoided altogether. Another study found that in urban areas the travel time savings through speeding were imperceivable so there would clearly be net benefits in travel times from reduced crashes through compliance with speed limits.

    1. Excellent, Michael… Thank you!

      When I have more time, I’ll look at the report with a view to creating a bespoke post specifically in relation to it.

  7. In India, we lose over a 1.5lac(150,000) lives annually to accidents. The major are due to SPEED.
    Speed need not be over the limit speed, any quantum of speed more than the control level of the driver is dangerous speed. In India a majority of fatal accidents, the victims are two wheeler riders, pedestrians, passengers of bus etc.
    A nationwide speed monitoring system is very much the need of the hour, and heavy penalty for rash driving with the first 48hours non bailable detainment will surely deter the idea of over speeding get away,
    safety first, every time….
    ps: we lose more lives to road accidents in a year than the deaths in all war in the last 50 years.

    1. Thank you for your welcome comment. The only point I would suggest is that “the control level of the driver” is arguably not the only constraint because the capabilities of the vehicle in relation to the conditions at the relevant time and place are relevant, too, especially if the driver is not the person responsible for the correct maintenance of the vehicle. Tyre condition during the monsoons spring to mind in this context, especially if one adds — dare I say — the poor overall standards in educating, training and testing drivers in India. And then there is the condition of many roads to be taken into account.

  8. Thanks to Eddie Warn. It is a very good article with VDO example. Stopping distance is proportional to square of the speed and the impact increases when speed increases.

    One minor thing we should consider is that reducing the speed limit cannot be done without also changing the environmental speed condition. Self-consciously drivers drive at a speed they feel comfortable (environmental speed). The environmental speed is governed by many factors, such as lane width, carriageway width, peripheral road side objects, combination of alignment, pavement conditions and general topography. It is to a section of road but not an individual geometric element. If we increase the difference between environmental speed and the speed limit then speed variance will increase. Consequently, the number of accidents at that section of road will increase.

    Therefore, if we want to reduce speed limit we must also bring down the environmental speed.

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