Safe Speed Forums

It comes up again and again. People, including Safe Speed users, keep telling me that "it's obvious" that there's a relationship between speed and crash severity.

Firstly we have to define "speed". It could be impact speed, average speed of vehicles or the speed of an individual vehicle. It could be measured in terms of appropriateness, in miles per hour or expressed as an excess over a speed limit.

Secondly we have to be realistic. Some might claim that we could drive a car into a tree at 20, 30, 40, 50, 60mph and the increasingly serious results would provide "proof".

Thirdly we have to have a purpose. That purpose is going to be to improve road safety through speed management if possible.

Now we have a purpose we can start to strip away some of the nonsense. We can strip away reckless and lawless driver behaviours because they are very unlikely to be influenced by speed management. It's only "normal motorists" who might be affected so we only need to consider "normal motorists".

Next we ask if there's a relationship between impact speed and crash severity, and it's clear that there is. I don't expect any arguments on that one! Effectively we can move "impact speed" to the other side of the question and ask instead: Is there a relationship between "speed" and impact speed for a normal responsible motorist?

But we haven't yet truly defined "speed". Are we talking about an individual or some sort of average? Are we talking about adjusted speed, free travelling speed or speed in relation to a speed limit? Do we frame speed in terms of appropriateness or in terms of miles per hour?

If we were to look at "appropriateness" where the full circumstances must be considered we'd fall out side the reach of speed management, because no speed management system can adjust itself to the conditions (apart from the driver himself of course, but that's another story.)

Since we'll have to evaluate our results across a population of speeds and outcomes, I'm going to assume that we're talking about an average speed, either resulting from one driver put to the test hundreds or thousands of times or we're looking at an average speed of hundreds or thousands of drivers all going through a particular test scenario.

Now what? It seems to me that we should test the behaviour and results by evaluating these defined conditions in relation to a couple of real world hazards. Firstly let's consider a sharp bend.

We're not going to make the usual mistake of firing imaginary driverless cars at the bend. We don't have driverless cars. Yet perhaps it's a particularly nasty bend that catches some drivers out - let's say that 1 in 1,000 drivers have been crashing on this particular bend.

What might we do to reduce the crash rate? One idea might be to impose a speed limit and another might be to put up some very clear bend warning signs.

Does anyone think that a speed limit might be the best solution? I certainly don't. When drivers crash on bends it's because they have failed to understand the bend and adjust their speed to it. If drivers had to rely on a speed limit to negotiate a bend safely, then any driver that missed the speed limit sign would be likely to crash. But we had 1 in 1,000 drivers crashing and I bet that 1 in 50 would miss or ignore the speed limit sign.

Can we dot the "i"s and cross the "t"s and make this into a logical dismissal of the original question?

What about using the same assumptions and a different scenario? I'm interested in the situation where someone "suddenly" pulls out of a side road into our path. How many of our test drivers would avoid the crash? Would adjusting "speed" alter the number who avoided the crash or the severity of the crash?

[more later]

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

What exactly do you envisage emerging from this Paul? Another page on the main site to which people will be directed when they try to argue that crash severity is determined by speed perhaps?
If so, I forsee that it will be a very complicated one, just like many of the others are, and will contain much substance that to many will appear esoteric. Naysayers will take one (as many as that?) look at it, get confused and ignore it, just like they do many of the other pages I'll wager. In fact, I'd stick my neck out and suggest that even some of the Safe Speed supporters in this forum who say they understand the underlying philosophy behind a particular assertion, do so becuase they want to believe any argument directed against speed cameras. Atually they don't understand it at all, its far easier to nod your head and say "Oh yes thats very good, proves the point precisely" than "Er actually I believe there's a flaw here because...." isn't it? As I've said before, call me Mr Cynical if you like.
You see the word 'misunderstanding' appear time and again, with respect to your work; it has done so in the latest correspndence with Mr Heavey. If such misunderstandings are commonplace, and they do seem to be, then perhaps it may be worth looking at how your case is presented? I hate to say this but.....dumb it down without losing the essence of what you are saying.

I occasionally drive in parts of North Wales, they have signs warning of the bend approaching as well as a speed limit sign specifically for that bend (not sure if this is compulsory, or recommended though).

Just a thought.

I'm interested at the moment, that's all. I've been exploring and analysing the subject and publishing anything interesting.

There are precious few folk even trying to do any top-level analysis of road safety issues and a series of false and oversimplified assumptions that need to be taken down.



Misunderstanding was a kind word - even a euphemism - to use in respect of Mr Heavey's report.

It'd be nice if there was a credible and simplified way to present the case. Unfortunately anyone who I might wish to convince will require details and evidence not assertions. That's where the complexity comes in. This seems like a fundamental limitation to me.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

If they're rectangular signs with a black border they're only advisory. Mandatory speed limit signs have to be circular with a red border.

But the absence of such signs doesn't cause you difficulties in negotiating bends that don't have them, does it?

_________________
"Show me someone who says that they have never exceeded a speed limit, and I'll show you a liar, or a menace." (Austin Williams - Director, Transport Research Group)

Any views expressed in this post are personal opinions and may not represent the views of Safe Speed

The model you propagate is complex for people to bother with. You it is hard even getting people on your site to share the same vocabulary. While you have useful points through your site, you are swamped with difficulites when it comes to boiling down your message to a soundbite. The best we can do is to use the SafeSpeed rules in conjunction with speed limits, not instead of them. Then we can work on sensible speed limit setting and improving road planning, and looking for ways to make speed regulation smarter and discriminating (and more just), without scrapping it.

_________________
I stole this .sig

No not at all, just thought I'd mention it, that's all. It wasn't supposed to be a criticism of what Paul was saying, although I suppose in the example he gave having both speed limit and warning sign would reduce crashes more. Maybe.

In Australia we have advisory speeds on bends where the speed limit is considered too fast for the bend. The signs are yellow with black numbers and are a very useful guide as to the severity of the corner.

As to what Paul is attempting, I agree that a "dumbed" down version is essential. I would suggest that the first link be to the "dumb" version and within the "dumb" version there needs to be a link to detailed explanations/examples of each point and a link to the detailed version as a whole.

I have to admit that I have only read parts of the site and basically use the forum to follow issues that I find interesting.

Maybe a nicer term would be "executive summary page" and "detailed analysis/data page" so that you could do a quick browse of the major points and if you take exception to any point or want to see the underlying reasons for the statement then go to the other link.

I actually failed a post graduate course I attended because I refused to pad an assignment with an extra 600 words. I asked the lecturer if I had missed anything and he agreed that I had covered the question completely. I asked, "so what do you want me to do, pad it?" He said "yes" and I failed the subject and never received the degree.

I think you can see from that example that I would rather use the least number of words to get my point across.

_________________
Ross

Yes I'm a hoon, but only on the track!!!!

Excellent post, basingwerk. I agree with every word. You really are coming over to our side aren't you.

In that case perhaps the corner specificiations out of rally driving would be a good idea? 6 is full speed ie the speed limit and 1 is a hairpin. They also give the distance away in metres or whatever. It would also work with the playstation generation as they understand the terminology from playing colin mcrae and its ilk.

I wonder if one could use gps technology and have a co-driver function in satnav? I am sure lots of us would welcome it on an unfamiliar nsl road. If it stopped working there is a danger more people would fall off the road more drastically so perhaps physical warning signs with an easy to understand corner direction and severity would be helpful.

I live here and the advisory signs indicate roughly half the speed one can drive the bend without drama.

Basingwerk - yes a really sensible post !

I have to comment that as a professional engineer I do understand Paul's treatises and agree with the theory when I read them, I have to think pretty hard before I can explain many satisfactorily to others. But the problem is that the subject is very complex and it is much easier and more attractive to take the campaigner's emotive soundbit stanace.

Which is why anti-speed campaigners have never defeated the substantive Safespeed cases using any logical arguments but resort to attacks and smears.

Then we agree. "More discriminating" speed regulation clearly demands that proper account be taken of the conditions at the time of the offence. Since no viable robot system can make a judgement with regard to immedaite conditions, they will have to go.

I'm quite sure you do know that I'm not calling for speed limits to be scrapped.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Er, anything to do with my comments on Tom Heavey's piece? If so, I should have said impact speed of course.

Should have read me own sig.

_________________
Make everything as simple as possible, but not simpler - Einstein

<giggle> I don't know in all honesty. I read a load of stuff yesterday, then I was working through the Heavey document, came across a fairly daft claim in this area and got distracted into a new view on the old speed / crash severity thing.

The first post in this thread is about 2/3rds of what I now have. I was working through the logic straight into a forum post. It would have been better as a web page, because there's still a fair little bit of development to go.

I'll publish it to a new web page as soon as it's ready.

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Absolutley no relationship, the Impact speed is defined solely by when the hazard was spotted, as this is the point when a driver applies the brakes, which defines the actual speed the vehicle is traveling at the time of impact.




very true, and a framework cannot carry such tolerances.




Simple signage, dangerouse bend ahead, at present we use 1 sign fits all, which does not supply enough information. Flash up signs, work better than speed cameras.



No, a general speed limit, might be very acceptable for the average car, however we have a vast range of cars, with differing ability. The road policy needs to keep up with the innovations and allow for the older vehicle.



The only concentration need to be on the driver that pulled out into someones path, which is our highest cause of accidents. If this element is removed, there is no accident to analyse.

_________________
Steve

Consider the case when a drunk suddenly strays onto your side of the road at 40 mph out of control and smacks into you as you start to brake. Consider the case of a child stumbling on the curb into your path when you are a few feet from them. Consider the case of a crossroads where someone doesn't see the give way sign and just ploughs across your path at 50 mph directly as you pass. Consider the case where your front wheel snags a ditch pulling you into an oak tree. In all these cases, and many more, speed of impact is full-on, and the relationship is 100%.

_________________
I stole this .sig

Clearly there is a relationship. In any given set of circumstances where a driver observes an obstruction which calls for emergency braking, the impact speed (assuming there is insufficient braking distance) will be higher if the initial free travelling speed is higher.

I think the question is wrong - but I'm not yet sure what it should be.

You're right that the worst case impact speed is equal to the pre-incident speed. i.e. no braking takes place because of the incident.

But there are still several huge factors that "disconnect" even these incidents from speed limit enforcement:

1) Many such crashes take place after speed has been adjusted downwards because of local conditions.

2) No imaginable system of speed enforcement will reduce the speed of all vehicles, so we might be talking about a crash involving a vehicle that has slipped through the speed enforcement net in one way or another.

3) Almost all such crashes are caused by the other party - but the concentration on speed means an opportunity to prevent the crash by comunicating with the at-fault party may have been missed.

4) speed limit enforcement has its greatest effects on open roads away from hazards where speeds would otherwise be highest. Since there are no hazards, there are no crashes.

5) The vast majority of all crashes do have braking before impact (one Australian study put it at 75%) and we also need to concentrate on minimising the effect of those by concentrating on "earlier perception").

(I think I had another really good one, but I've been interrupted by the phone and it's gone. I'll add it latter if it returns... )

_________________
Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

The traveling speed does not effect the accident taking place or the impact speed.

A driver that pulls out of a side turning, determines the impact speed, based on how much reaction time is available to victim, being the driver that had the right of way.

Traveling speed has the same effect as where the accident happens, in a 30, 40, 50, 60 or 70 mph limit. Neither of these can be pre- judged.

Then their is the differance between a driver paying attention and one who is not.

For instance:

A driver not paying attention, traveling at 30 mph will have a higher impact speed than a driver traveling at 60 mph paying attention to the approaching hazards.

_________________
Steve

We could be legally driving at any speed limit, when this happens.


Consider the case of a child stumbling on the curb into your path when you are a few feet from them.

Same again, the fault being that of a parent



Again the speed limit is variable, thus our traveling speed is variable, the only relationship is therefore when the drunk runs into our path, when the child steps out in front, and when the person chooses to ignore the give way sign. It is only this relationship of the error that equals the impact speed.



Not heard of a ditch jumping into the road too often

_________________
Steve