Speed has ‘direct influence on crash occurrence and severity’

08.23 | 5 April | | 23 comments


Governments need to take actions that will reduce the speed on roads – as well as speed differences between vehicles sharing the same road, a new report has found.

The International Transport Forum* (ITF) report, titled ‘Speed and Crash Risk’, concludes that with higher driving speeds the number of crashes – and the crash severity – ‘increase disproportionally’.

The report points to research which suggests that the risk of death is about 4-5 times higher in a collision between a car and a pedestrian at 50kmh – compared to the same type of collision at 30kmh.

The report recommends that where motorised vehicles and vulnerable road users share the same space, such as in residential areas, 30kmh (20mph) is the recommended maximum speed.

It also suggests stricter enforcement or an upgrade of the infrastructure is needed to compensate for the increased risk related to higher speeds.

The report has been welcomed by the campaign group 20’s Plenty for Us.

Rod King MBE, founder and campaign director, said: “This is yet another report coming to the firm conclusion that 20 is plenty where people live, work, play, shop and learn.

“Other countries have adopted a near universal 30km/h limit for urban and residential streets.

“Over 25% of the UK live in authorities who have also set 20mph as the right urban limit. The Scottish Parliament is considering a bill to make 20mph the limit (with exceptions) for built up roads.

“It’s time to end the postcode lottery on pedestrian/cycling safety and general well-being in our residential and urban places by setting a 20mph default limit for built-up roads across the UK.”

*The ITF is an intergovernmental organisation with 59 member countries. It acts as a think tank for transport policy and organises an annual summit of transport ministers.


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    It is a shame that it comes across that some people believe there is only the one problem that they concentrate on which needs solving to prevent collisions. Collisions have for a long time been described as “rare, random, multi-factor events”. There are several factors in most collisions in my experience – some have fewer, some have more.

    One thing I will say in regard to speed. The higher the relative speed of the two objects the more kinetic energy there is to transfer – a real problem when it transfers to a living creature. The amount of kinetic energy available for transfer increases with the square of the velocity (think that is mathematically correct) then reducing the average speed of vehicles involved in collisions will reduce by a greater amount the damage causing kinetic energy. A good thing.

    Which of the following two scenarios would you prefer to be in? 1) A passenger in a car exceeding the speed limit but being driven by someone who is “looking where they are going” or 2) A passenger in a car being driven at or below the speed limit but whose driver is not looking where they are going?

    Multi-factor events = multi discipline solutions. Stop arguing and start collaborating.


    Nick, Preston
    Agree (1) | Disagree (0)
    +1

    Doesn’t matter whether the vehicle is driven by a human or an autonomous one. If someone suddenly and unexpectedly walks in front of one with too little or no opportunity to brake or no opportunity to even think about braking then the end results would be the same. That said, with the giving of safe space and the improved visibility that it affords a driver might see the pedestrian and perhaps their close proximity to one’s approach and would therefore be able to take evasive actions before the pedestrian actually steps off the kerb and in front of one, and if unable to avoid a collision then to some degree the injury would be mitigated by such an earlier reaction. No argument there.


    Bob Craven
    Agree (5) | Disagree (0)
    +5

    Okay for safe following distances Bob, but not for unexpected appearances in your path by of other road users, such as in the recent fatal collision between an autonomous vehicle and the pedestrian in Arizona – the technology didn’t work there.


    Hugh Jones
    Agree (3) | Disagree (1)
    +2

    I agree Duncan a stopometer would be a very good idea. Like a radar or laser beam that could slow a car down if too close to the vehicle in front but not one that can be manually set but one that is automatic. Therefore it won’t matter if the vehicle in front is 10 ft or 300 ft ahead at speeds between 5 to 70 mph. With the required information of full stopping distances input the vehicle can and will slow a prospective tailgater or otherwise negligent or dangerous driver to be at last that safe distance. This would also be valuable on tight corners and bends in the country where the car takes over the speed control and automatically slows the vehicle down rather than run into the bend too fast and lose control. Such a device in the urban scene will have the effect of giving space and therefore clearing visibility for all road users and an end to the clogging up of roads and the streams of congested traffic. If used by HGV hauliers it will stop their endless frustrating tailgating and overtaking causing rolling road blocks that goes on and will reduce the risk of pile ups as all vehicles will be automatically the correct safe distance apart and with brake assist will be able to slow and stop without collision.

    Yes an extremely good idea Duncan and based on the principals of safe following on or stopping distances. Then no one will be instructed by ADIs to be only the following on distances whilst learning to drive.


    Bob Craven
    Agree (3) | Disagree (2)
    +1

    From what Pat and Charles say a “Stopometer” would be a much more appropriate instrument than a speedometer wouldn’t it?


    Duncan MacKillop, Quinton
    Agree (4) | Disagree (2)
    +2

    Not being able to stop, distance to stop in and safe space all have an important message for road users and especially for those driving vehicles and riding powered two wheelers. However we are not setting out to write the rules of the road or to design our road infrastructure from a blank sheet of paper.

    Like it or not, the current system is that the road is NOT a safe place in principle, motorised vehicles do have dominance and human error is a factor in 94% of collisions. Road safety education has to continue to be about all road users taking care, especially by those who are most vulnerable. The road is not a place of equality for all and until it is (if ever) road safety education should continue to teach both children and adults to take care, be alert and learn to avoid placing themselves at risk of injury by managing their exposure to risk.

    Utopia won’t be built in a day and ‘novel’ forms of road engineering and pedestrian and cyclist ‘rights’ for equality with motor vehicles have a distinct risk of putting users in harm’s way until the current culture of the roads changes. We can and do “tinker around the edges” with road design, however the conundrum is that road culture is not likely to change unless roads physically change but just changing roads physically won’t change the culture. There are many ‘pie-in-sky’ ideas but I’m not aware of any workable solutions for that one.


    Pat, Wales
    Agree (9) | Disagree (5)
    +4

    Hugh, you are a genius Sir! “Not being able to stop” – that is *exactly* what we need to target and attempt to eliminate. It applies equally outside schools, on shopping streets, on housing streets, on rural A-roads and lanes and on motorways! It obviously has two components: speed and distance. But, unfortunately for some, it also reveals that speed limits are totally useless to tackle it with, and could even be regarded as making the problem worse. Driving at 20mph past a stationary bus or through streets with crowded pavements would be criminally reckless, where you might reasonably expect no more than two or three feet to stop in – if, say, a pedestrian walks or stumbles out in front of you. Sure speed is a factor, but uncoupled from distance-to-stop-in it is meaningless. Let’s keep it simple, honest and correctly focused and drop the obsession with speed and target the real problem: “Unable to stop”!


    Charles, England
    Agree (10) | Disagree (2)
    +8

    Yes Andrew, picking up on your tongue-in-cheek comment on motorways, isn’t it peculiar that the roads with the fastest speeds are statistically amongst the safest? It is safest for pedestrians as well as they are banned.

    Perhaps we should ban people from walking near all roads with a high crash risk “for their own safety”. Mind you that would be as silly as expecting people to abide by 20mph signs without police or engineering.


    Pat, Wales
    Agree (10) | Disagree (2)
    +8

    Perhaps substituting ‘Not being able to stop…’ for ‘speed’ in the above headline would appease those still in denial? Still a rather obvious statement, but a necessary simplification for some.


    Hugh Jones
    Agree (4) | Disagree (1)
    +3

    Just a thought: given the foregoing, should we restrict speeds on motorways to 20 miles/hr?


    Andrew Fraser, STIRLING
    Agree (7) | Disagree (9)
    --2

    I would also have thought that it would have been the distance between the two objects that could determine just how fast a vehicle hits another and that of course will give different inputs depending upon the impact speed and the nature of the object hitting and hit..

    So space is, or has to be, always in the equation as in most cases there is a relationship between space and speed. Therefore the giving of insufficient space can act upon any situation and the fact that by the giving of too little space the missing of an object could not be guaranteed.


    Bob Craven
    Agree (5) | Disagree (1)
    +4

    The problem with your opinions, Hugh, is that the policies based on them have not been demonstrated to work. It’s the same problem in the above report. They present similar opinions to you, but go on to make many statements that appear to be false. Eg, here are just two of them:

    p8: “There have been a number of research efforts undertaken in the last few decades which have all shown … when speed increases, the risk of a crash and of its severity increases”.

    p7: “Experience worldwide has proven the effectiveness of automatic speed control systems in reducing speed, and in turn road crash frequency”.

    Both of the above are not true. The authorities have always refused to run RCT scientific trials for “automatic speed control systems”, and no official report has managed to remove all selection effects. This means that there isn’t even accurate evidence, let alone proof, of road safety improvements. Further to that, several independent reports have managed to remove all selection effects and they found increases in fatal and serious crashes at automatic speed control sites.

    Do we want the policies that affect our safety on the roads decided by the opinions of those in authority, or do we want evidence-based policy? If the former, then be honest. If the latter, then start running RCT scientific trials.


    dave finney, Slough
    Agree (12) | Disagree (7)
    +5

    It’s the laws of physics Dave. These are already widely accepted without scientific trials i.e. the speed (of a moving vehicle or vehicles) has ‘direct influence on crash occurrence and severity’ – I don’t think that can be in dispute and doesn’t need further evidence, trials or investigation to prove it – nor can it be just the author’s opinions, as it is a known fact. The speed of a vehicle immediately before a potential collision, is the biggest influence on whether contact is made or, whether it is avoided and if not avoided, the severity – it is not rocket science, but it is science. It would be like you asking for RCT scientific trials to substantiate claims that gravity actually exists.


    Hugh Jones
    Agree (16) | Disagree (4)
    +12

    It is illegal, I believe, for private companies to make claims for their safety products/services without robust evidence to support their claims. Why is it then that authorities do not ensure similarly high standards of evidence for the safety products/services that they sell to us?

    The above report contains nothing new, simply the authors opinions, supported by reports from other countries (non in UK). In all of the reports they cite there were:

    No RCT scientific trials
    None managed to remove all selection effects from the results

    The evidence the authors present appears, therefore, to be of poor quality.

    High standards of evidence are demanded for private industry. When are the authorities going to start applying similar high standards for government policies that we then have to bear the cost of?


    dave finney, Slough
    Agree (14) | Disagree (10)
    +4

    A better and more appropriate analogy Charles is to liken the wealthy householder who becomes the innocent victim of a burglar, to a pedestrian, cyclist etc. who becomes the innocent victim of a speeding motorist. Obviously we take action against the offenders i.e. the burglars and the speeders respectively and not the victims i.e. the wealthy householders or the vulnerable road users.


    Hugh Jones
    Agree (7) | Disagree (4)
    +3

    Hugh, yes your headline would work too, but be equally unconvincing – as in my analogy it is the hypothetical crime of having wealth above a certain limit that is analogous to driving at a speed above a certain limit; that is, it has been arbitrarily criminalised in the same way and become an irrational obsession in the same way.


    Charles, England
    Agree (4) | Disagree (9)
    --5

    Duncan: ‘…by far the greatest number of fatalities happen at low speeds…’ Do you mean vehicle occupants or vulnerable road users? How do you know this anyway? Where does your data come from, never mind theirs! Perhaps you mean, by the time contact was made, the speed was technically ‘low’ when compared to the too-high a speed the vehicle(s) had been travelling at moments before, in which case the ITF’s assertion is correct about more stringent speed management needed (which we knew anyway) or.. the vehicle(s) were already travelling at a ‘low’ speed (definition?) before impact, in which case fatalities would have been unlikely.


    Hugh Jones
    Agree (9) | Disagree (2)
    +7

    Interesting analogy from Charles. One could change the above headline to ‘Level of criminality has direct influence on burglary and occurence’. It’s still stating the obvious. Capping the criminal behaviour however – NOT the wealth – reduces burglaries and their severity.


    Hugh Jones
    Agree (5) | Disagree (5)
    0

    Interesting quote from the introduction to the report. “with lower speeds the number of crashes and the crash severity decreases”.

    By far the greatest number of crashes are low speed fender-benders and by far the greatest number of fatalities happen at low speeds so where on earth do the authors of this report get their data from? Last time I looked there were around 2 million ‘energy exchange events’ every year in the UK a fact which keeps many thousands of body shops in business.


    Duncan MacKillop, Quinton
    Agree (10) | Disagree (4)
    +6

    If one looks at CRASHMAPS on the Web one can clearly see that in residential areas and quiet streets there are no more than 5% of recorded incidents/collisions. A further 5% approx. are on Motorways and the remaining 90% are generally on main arterial roads and routes through towns and cities and from them into the countryside. Even where 20 mph meets 30 mph at junctions they are classified as being in a 30 mph area even though they have emerged from a 20 mph area.

    The vast majority of these collisions or incidents on main roads with numerous side streets and on roundabouts involving vehicles at various speeds, some over but mainly most under the speeds posted. Although the speeds may vary all have the same thing in common and that is of a lack of safe space and a lack of understanding of the full stopping distances. Stopping distances involved at speeds of around 30 mph in towns where the safe distance is between 75 and 90 ft.

    Why is that one might ask?


    Bob Craven
    Agree (10) | Disagree (2)
    +8

    The conclusions of this report might deserve some respect, and even carry some weight, if the study was a neutral and unbiased look at *all* the significant factors influencing the frequency and severity of road collisions, and from that concluded that traffic speeds were the most significant factor. But as it only looked at one of the many possible factors, traffic speeds, then they do not. It doesn’t even explain why speed *is* its focus, rather than one of the innumerable other factors that can influence the crash risk.

    Try this little experiment, and see if you agree with its conclusions and recommendations. Take the featured report and substitute the concept of “road crashes” with the concept of “home burglaries” and substitute the “traffic speed” factor with the “household wealth” factor. Would you support the conclusion that the solution to home burglaries is to find ways of capping household wealth and exploring the punitive measures that could be used to ensure that householders were not flouting the cap? Even after realising that burglary rates rise disproportionately in areas with increased household wealth?

    Sure, and probably even from the results of the above experiment too, there will be some people and associations of like-minded and equally ill-informed and blinkered individuals for whom the report adds baggage to their band-waggons, and who will be clamouring for the recommendations to be implemented. But given the arbitrary and narrow scope for the “research”, it is inconceivable that following its recommendations will lead to anything other than the inevitable “garbage in, garbage out” result.


    Charles, England
    Agree (16) | Disagree (12)
    +4

    Thanks to the ITF for telling us what is already widely known. I see they’re referred to as a ‘Think Tank’ – hope they didn’t waste too much time ‘thinking’ about this one.


    Hugh Jones
    Agree (15) | Disagree (6)
    +9

    The ACTUAL speeds on roads along with the road user hierarchy, safety of each user group and traffic volumes are the most important. Discussions about posted speed limits often muddle the matter when many roads with 30mph limits have actual vehicle speeds in the low 20s and many 20mph speed limits have a high level of non-compliance.


    Pat, Wales
    Agree (22) | Disagree (3)
    +19