How to design a city?

Michael, this is definitely not true. Speed is most certainly a major contributory factor in many (though of course not all) collisions and this is backed up by copious research, e.g. a much-misquoted TRL report.

Yes, I agree, what I was trying to say was that travelling 70mph on a motorway should be perfectly safe, but travelling at 70mph in a 30mph zone is normally unsafe (I say normally as there are some ridiculous open stretches of road around with a silly 30mph limit). Motorways are the safest roads of all, and basically the lower the speed limits, the higher risk on a road, I know that sounds obvious, but I can't stand it when all this research is done and they put "Speed Kills" at the top in huge letters. Yes, I know there are more oppurtunities for collisions on 30mph roads than motorways, but I just wanted to make that point against the "Speed Kills" believers.

It is really not a solution to just improve driver skills and reactions. It needs to be at least coupled with a commitment to drive slowly. High skill levels among drivers, paradoxically, can cause higher speeds. What matters is the degree of commitment that they have to driving in such a way that does not cause fear and road danger. Plus, some highly skilled drivers, e.g. racing drivers driving in normal traffic, exercising their skills can scare the living daylights out of other, less skilled drivers.

I do disagree with this a little, in my experience (obviously I can't speak for all) but most high skilled drivers are very safe on normal roads as they observational skills (in my mind, probably the most important skill in a driver) are excellent, same goes for racing drivers, it would take a very irresponsible racing driver to push their limits in public traffic. When I said about improving driver skills, I wasn't talking about cornering skills or things like that, I was talking about (as above) observational skills, reaction times (i'm sure you all know the kind of person who half pulls out of a side-road, wait until traffic is almost on top of them, then pulls out of the side road, very frustrating).

The key is always, always, to reduce road danger at source. That means avoiding high speeds in the first place, not attempting to manage them using second-best sticking plasters.

Someone hit by a car doing 20mph has a 95% chance of survival and only a 55% chance at 30mph. The vast majority of those who survive a 30mph crash will sustain serious injuries.

Also beware of the word 'accident'. It doesn't do justice to the fact that rates of collision are almost built-in system features rather than accidental. Collision rates have gone down gradually but often at the expense of people shying away from cycling and walking and using some sophisticated statistical comparisons haven't improved much in the last fifteen years.

This may seem a bit pedantic of me, but high speeds are not a problem, excessively high speeds usually are, take my example in the first paragraph. I'd say that survival statistic is pretty accurate (i'm guessing it's for car/ped collisions) however, there is no situation where cars and pedestrians should be on the same tarmac, this may sound ignorant of me but I don't mean it like that, but I tend to not pay (relatively speaking) a huge amount of attention to those. True, I am still in the habit of using accident instead of collision (have to watch Hot Fuzz a few more times). In short, I try not to pay much attention to statistics unless I have got the data myself, as it will have no doubt been twisted in some shape or form between collection and presentation.

Apologies for the long reply.