You are reading a single comment by @bq and its replies.
Click here to read the full conversation.
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
@bq
This is a very good question. All models which suggest 20mph would make things better assume that such a limit would be obeyed. As no driver in London obeys the 30mph limit unless they have to this is an unwise assumption to make.
I accept the argument that if motor traffic was doing 20mph their journey times may actually improve. Traffic flow improvement can be counter-intuitive sometimes. But how do you make it do 20mph?
Though it would have a small effect on cyclist deaths by HGVs which have almost all been very low speed incidents at junctions and traffic lights.
However, we all know that the average speed of cars in London is 12mph. This means that average speed cameras won't work, as even with 50mph bursts between cameras, the likelihood of recording an average of above 20mph is slim. You would have to litter the city with cameras to cover every junction as well, or they are useless. The money simply isn't there.
Static speed cameras (e.g. Gatsos) are not only useless, but a menace to safety, as drivers simply drive as fast as they like, then slam the brakes on as they go past the camera.
You couldn't employ enough traffic police to do it.
Which leaves us with what we have now - self enforcing 20mph zones by means of "traffic calming" measures. All of which, in my opinion make cycling more dangerous, not less.
So what we would probably end up with is a 20mph limit that was routinely ignored, and either cars would "speed" at 30, rather than at 40 or 50 as happens now, or they would continue to speed at 40 or 50 and drivers would have even less respect for speed limits in general than they do now.