Speech to Speed Congress 2010 by Mary Williams OBE, Brake CE

Is there a safe speed at which to crash a vehicle into someone on foot or bicycle? Is that speed 6mph? 4mph? Imagine blindfolding a child and telling them to run at 4mph into a lamp post. Commonsense tells us there is NO safe speed at which to crash. Crashing at any speed can result in death.

[SLIDE] History agrees. The earliest vehicles travelled at little more than walking pace but still caused death. As we know, when Bridget Driscoll, Britain’s first known person to die, was killed in 1896 it was by a car described by witnesses as travelling at a tremendous speed: 4mph. At any speed, an impact between a soft human body and something much harder, generally made out of metal or at best dense plastic, can be lethal or cause paralysis or brain injury. It is also critical to remember that the potential damage caused by impact is only part of the story. Vehicles crush as well as impact. Any vehicle, whether it is a one tonne car or a 32 tonne truck has the potential to kill through its crushing power, either because a victim has gone under that vehicle’s wheels, or because the vehicle has flipped over on to the victim. Picture the toddler in a buggy crushed under the wheels of a slow moving but left turning vehicle that mounted the pavement.

This is of course all basic stuff that you and I know. But the point is not to teach you to suck eggs, but to help us all think about inadequate driver perceptions of the killing power of vehicles and speed, and how that translates into poor driving attitudes to speed and drivers driving far too fast, particularly, in the context of this session, in towns and villages.

[SLIDE] Today Brake is releasing findings from our most recent survey of about 900 random UK drivers’ speed behaviour. Almost three quarters (72%) drivers surveyed admitted driving at 35mph or faster in a 30mph zone. Half of these offenders (36%) admitted doing this daily or at least once a week. And as we have heard this morning many UK drivers also break posted 20mph limits in areas where enormous and commendable efforts are being undertaken to communicate and enforce these limits. So why do so many drivers still think it’s OK to break even a 30mph limit let alone a much more appropriate 20mph limit? It is highly likely that in the UK many drivers still have a dangerous and false perception that driving ‘a few’ miles faster – for example 35mph in a 30 - is only breaking the limit by ‘a little bit’, and that this won’t make much difference to their safety.

[SLIDE] Understandably, Britain’s government-run Think! campaign focussed significantly in the past on countering this false perception through the arguably over simplistic and potentially misleading strap line on posters that ‘at 35mph you are twice as likely to kill a child you hit as at 30mph’. Unfortunately, this strap line can wrongly infer that it is OK, or at least significantly ‘better’ to hit a child on foot at a collision speed of 30mph. Hit at this speed a child is still likely to die or be seriously maimed as I will demonstrate later. Most importantly of all, this strap line certainly doesn’t address the need for drivers to think about stopping distances and the over-riding importance of stopping in time to avoid crashing, rather than crashing at a slightly slower, but easily still fatal speed. In addition, the strapline leaves the door open to criticism from people that must not be given such easy opportunities. The despicable pro-speed group Safe Speed says on its site: “It isn’t true that you are twice as likely to kill a child by driving at 35mph. (It is true that you are twice as likely to kill a child in a 35mph impact as a 30mph impact. But very few pedestrian impacts take place at free travelling speeds.)” I presume by free travelling speed they mean in this context the speed of travel prior to reacting to any hazard. What’s insidiously wrong with Safe Speed’s statement is that, like the Think! campaign, it implies that it is OK to hit a pedestrian at a lower speed – by this I mean, and presumably Safe Speed means, the residual, or impact, speed that a vehicle is travelling on impact after the driver has reacted (or thought), and then braked (if indeed there is time to do so). Safe Speed do not of course explain that the impact speed of a vehicle originally travelling at 35mph or 30mph that hits a child at a defined distance can still cause death and catastrophic injury. They do not explain that the faster you go, the more you are likely to be involved in a collision (see University of Adelaide reports et al).

[SLIDE] The Think! campaign more recently has addressed the issue of impact speeds. A more recent statement on the Think! website says: “At 30mph, if a child stepped out 25 metres ahead of you, you’d hit them at 19mph. At 40mph, you’d hit them at 38mph – twice as fast.” This is surely a step in the right direction, but far from satisfactory. It can still be implied from this statement that an impact speed – in this case 19mph - is acceptable. Is hitting a child at 19mph in any way OK? Absolutely not. Another problem with this statement is the choice of the 25 metre marker: this is far too great a distance (about six car lengths) for safety in communities. Less than half this distance, the 12 metre marker (about three car lengths), is a far more appropriate perameter. For anyone who knows their stopping distances chart this is of course the distance within which a very vigilant car driver with fast reactions would hopefully stop if driving at 20mph or lower.

[SLIDE] Stopping distances are of course made up of time taken thinking and then braking. You will know that as speed increases, thinking distances increase at a proportional rate as you can see from the chart. For the purpose of the stopping distance chart in Britain’s Highway Code, the thinking distance of 0.67 seconds has been used. It should be noted that by anyone’s standards this is a fast reaction time and must therefore be considered a bare minimum. While thinking distances increase at a proportional rate to speed, braking distances increase disproportionately at a much greater rate than speed. The easiest way to explain this to any member of the public with a GCSE in maths is that braking distance to a full stop is proportional to the square of the initial speed, not the initial speed.

[SLIDE] As this slide shows, it’s also worth noting that a vehicle travelling at any initial speed will still have about 70% of its initial speed when it is half way through its braking distance. Using the example of a car travelling at 20mph on this slide, you can see the lack of any drop in speed during the six metre thinking time, followed by a convex curve for the following six metres, which shows that at the nine metre marker – half way through the braking time – the speed is still above 13mph with only three metres to go before stopping completely. You get the same shape of line for any speed you plot. Yet another way of explaining the importance of stopping in time. Those playing ‘devil’s advocate’ may argue that it is pie in the sky to think that urban speed campaigns should focus entirely on stopping in time, rather than crashing at lower speeds. Brake disagrees, along with anyone else who takes a zero tolerance approach to crashes.
Using the 12 metre marker as our maximum stopping distance in towns and villages (obviously with a shorter stopping distance being even better), we can do some interesting mathematical calculations that can help the public understand the importance of stopping in time, as I will demonstrate.

[SLIDE] If a car is travelling at 30mph, rather than 20mph, then that car’s impact speed at the 12 metre marker is still about 27mph. The car will hardly have slowed down at all because three quarters of the 12 metres will have been taken up with thinking or reacting time, as of course the stopping distances chart shows you.

[SLIDE] Why the famous picture of Jacko? We can use this impact speed of 27mph to calculate the height that a child would have to fall to attain that speed, using the equations of motion under constant acceleration. This can help gives the public a very real sense of the danger being posed.

[SLIDE] Using the average acceleration due to gravity as measured at the surface of the earth, a child falling backwards out of a third storey window, or from the top of a gabled roof of a two storey house, would hit a concrete pavement at about 27mph. Clearly an event likely to cause death or serious injury. I say falling backwards to emphasise the vulnerability of the head, but also to indicate lack of any opportunity for the victim to control the nature of the impact. I say a concrete pavement to indicate the contrast between soft flesh and hard vehicles.
So, in plain English, if you drive at 30mph, and a child runs out three car lengths ahead of you, the damage you will cause that child is the equivalent of them falling backwards out of a third storey window (and that’s not counting the damage your vehicle or someone else’s vehicle may cause by crushing the child to death).

[SLIDE] Now if we consider the same car being driven at 36mph, then that car’s residual speed at the 12 metre marker may not have reduced at all – the car would possibly have slowed down by 1mph to 35mph if the driver has good reactions, but nearly all, if not all, of the distance will be taken up with thinking rather than braking. (Certainly as speeds approach and then exceed 40mph there is absolutely no chance of the driver reducing their speed at all by the impact distance of 12 metres.)

A residual speed of at best 35mph is inevitably catastrophic to the human body. Using the same calculations, this is the equivalent of a child falling backwards out of a fifth floor apartment onto concrete. No-one would expect a child to survive that fall.

This clearly demonstrates the stupidity of Safe Speed when they say that ‘very few pedestrian impacts take place at free travelling speeds’. In fact, any driver choosing to drive at 36mph or above who hits a child 12 metres in front of them is almost inevitably going to be travelling at their so-called ‘free travelling speed’. Parents don’t let their children hang around on fifth floor window ledges. But many drivers in the UK, many of whom are parents, do drive above 30mph in their own communities. This is a comparison everyone can understand.

[SLIDE] This slide shows some chosen impact speeds at the back and the calculated height of fall at the front. You can see that as the impact speeds go up proportionally at the back, the calculated height of fall for these impact speeds is beginning to pull away and increase disproportionately.

[SLIDE] A word on pedestrian protection measures. It is often the case that pedestrian protection measures, such as so-called pedestrian-friendly bumpers, are mentioned in the same breath as car occupant protection measures. In many ways, these two sets of measures are far from comparable. An occupant is in a contained space and can be protected in that contained space by air bags. A pedestrian is outside and can fall any which way, including under the wheels of the vehicle that has hit the pedestrian, or, indeed, a different vehicle.

To quote EuroNCAP’s website, “although it is possible to control the point of impact of the bumper against the pedestrian’s leg, it is impossible to control where the dummy’s head will subsequently strike.” While Brake would not argue that development of pedestrian protection measures, particularly very soft ones such as exterior air bags, is pointless, there are so many variables for pedestrians that their effectiveness will always be variable too. Such protection measures will be most effective at the slowest speeds, and even then will not counter the damage that can be caused by being crushed by a vehicle. It’s also worth sparing a moment to consider the argument that better brakes in modern vehicles means stopping distances are shorter. There are a lot of variables here. Stopping distances can be affected by weight and loading of a vehicle, and the maintenance as well as the design of the brakes. They can be affected by variations in drivers’ reaction times and by weather conditions such as wet or icy roads. Any driver who buys their vehicle on the basis that it has the best possible braking technology is doing pedestrians a favour, and could be charitably thought to be buying that vehicle partly for moral reasons. That moral high ground flies out the window if that driver then treats their brakes as a licence to drive faster. Anything we can do to decrease stopping distance – whether it is driving slower or buying a great car – should be done. It’s not an either / or deal as the objective is to stop in time to prevent a crash.

Thinking a moment further about driver campaigns, there have been many campaigns in many countries that have chosen, based on research, to focus on motivators other than not killing someone. For example, campaigns that focus on the chance of being caught speeding and consequently losing your licence or your job.

[SLIDE] Most recently, the Think! ‘Live With It’ campaign has chosen to refocus on the human devastation caused by speed by considering a driver who has to live with the knowledge that he killed a young boy. The over-riding concern of any crash is potential casualties, so Brake is pleased to see this direction which demonstrates perhaps a renewed hope that many drivers may at least be prepared to attempt to translate concern for their fellow man into changes in behaviour.

So what are the implications from this paper for Brake’s urban speed policy and our education and media campaigns and potentially yours?

[SLIDE] Brake will continue to advocate a default 20mph limit for all towns and villages with the objective of total prevention of all collisions with hazards that appear three car lengths or more ahead. We will press for continued roll out of speed cameras and, better, ISA to be introduced. This is the only and ultimate solution to law breaking speeders, and we must maintain the pressure on politicians – particularly in Britain during such turbulant political times and in light of a Conservative-led government that has stated in opposition its intention to halt speed camera expansion.

To encourage more flourishing and safe community space, we will push for more vehicle exclusion areas, where people can move freely around central community facilities and green spaces without fear of traffic. These are preferable to so-called naked roads where road signage and pavements are removed and space is shared between people and vehicles, which has come under so much criticism in particular from campaigning charities representing the blind.

We will use our education programmes in schools and companies, and our campaigns in the media, to talk more about the maths of speed, to help drivers better understand the need to drop speeds so they can stop in time, while also continuing to ensure that the stories of the bereaved and injured families are heard widely and loudly. We will continue to emphasise the vulnerablity of children, the disabled, elderly and cyclists in towns and villages, explaining that these people make up the fabric of communities and deserve the best possible protection and not the death penalty for their mistakes. The theme of this year’s Road Safety Week is Kids Say Slow Down. Need I say more.

Tags: speed crash vulnerable road users speech