Safe Speed Forums

I don't know how 'baked' this idea is, but I want to understand how we have speed limits set at deadly levels.

What do I mean?

Take the Joksch rule of thumb affecting the probability of death of car drivers. Joksch suggests that the probability of death is approximately 1.0 at 70mph crash delta V. In other words if we hit something hard at 70mph we're pretty much certain to die. See this page for details on the Joksch equation. So why do we have 70mph as a national speed limit?

Then there's the 30mph limit in town. We're told that it's set to protect pedestrians - yet if we hit them at 30mph many of them die. Depending on which research you prefer it's between 1 in 5 and 1 in 25. So 30mph is a deadly speed. See this page for a discussion on '30mph is a deadly speed'.

Isn't the entire concept of speed limits undermined if we set them at a deadly level? What's wrong with this picture?

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

I suppose it's because there has to be a compromise somewhere. 30mph limits offer pedestrians some safeguarded against being killed through their own inattention, whilst permitting traffic to make progress at a reasonable pace.
Colliding with another vehicle or stationary object at 70mph could, and sometimes does, prove fatal yet we're happy to see the limit raised further still.
It's a question of balance isn't it?

I'm not really sure (which is why this is in the brainstorming forum), but I think my underlying point is really that speed limits are NOT set at the sort of levels that would deliver the safety that they are supposed to deliver.

It's the 'something else delivers the safety' argument from the opposite direction.

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

I believe, despite what they say about setting speed limits for "colision-safe" speeds, that they are in fact setting limits at what would be the upper end of an appropriate speed for a typical hazard density in the dry for a relatively inexperienced driver or one with tunnel vision and for a car with as much accident protection as a wet cardboard box (ie, one designed in the sixties)
I have recently succumbed to varifocal glasses - though not for driving (unless I forget to swap them over). I have once or twice forgotten to swap them over and .. I have a hypothesis looming that embraces the above. I will formulate my thoughts over the next couple of weeks and post separately.

If pedestrians and other road users always stayed in their designated zones, the question probably wouldnt even arise.

In terms of history, speed limits were plucked out of the air as something that "seemed appropriate" and subsequently legitimised. I don't think either the 30 mph urban or 70 mph NSL were originally set on any kind of scientific basis.

The theory behind them is, AIUI, that they should represent the speed at which a driver should be able to stop in time to avoid any kind of hazards he is realistically likely to encounter.

_________________
"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

This is a similar argument to, "you're almost guaranteed to die if you fall from 100ft, so why do we allow aeroplanes to fly at 35,000ft?" - the point being that safety is dictated, not by the height, but by the remoteness of the possibility that the aeroplane is going to fall out of the sky.
Current road safety practice is like limiting planes to 100ft altitude, while doing nothing about the things which make them fall from the sky - in fact, limiting altitude to 100ft would make it far more likely that a plane is going to hit the ground, but this is perhaps taking the analogy a bit too far.

I don't believe that speed limits were originally meant to be strictly enforced, but rather as a means to 1) enable the prosecution of dangerous driving, and 2) to protect the public against possibly erroneous subjective judgement by the police.

Regards
Peter