BBC under fire over programme about "how best to share" the roads, titled... "Should cyclists stay in their lane?"; Cycling campaigns urge government to "hold their nerve" on 20mph speed limits + more on the live blog

On your last point - ain't that just the problem?  Mass motoring means we're effectively letting people who are not suitable drivers in.  Or - to be fairer - a one-off test is no guarantee of continued competent, safe driving.  Especially not over a lifetime!

I happen to think it's probably easier to engineer out issues rather than raising the average skill level (and more importantly - average concentration / alertness) of all drivers.  (I think we agree on this in regards to speed limits and road design).  Unfortunately that will take us a very long time to do!  But in the mean time, if some psychological hack can be shown to make things safer and (slightly) more pleasant (like just reducing a number - because people see those as targets) why not?

Many people already drive like their speedo broke.  I simply don't think changing from a pretty arbitrary 30 to 20 (after a period for adjustment, because "change!") will bring about the end of civilisation given that people pay any notice to speed limits.  Which they mostly do!  Albeit they clearly don't think the "maximum" part is very important (almost like they consider them targets), nor the concept of "drive to the conditions".

The misconception here is that people drive at 30 because they're used to it, 30mph is the speed most people would not significantly exceed in urban areas in the absence of a speed limit, most people want to not crash or run people over and drive accordingly.
People defaut to the speed they feel safe driving, and that's more down to how our brains work rather than due a wilful desire not to follow the law.
That's also why there's some generous urban 40 limit roads with average speeds barely over 30mph. It works both ways, you can tell drivers they can go faster, and they still don't.
This is not to say dropping speed limits can't make a difference, for what difference limits can make to actual traffic speeds, they're most effective when they match the design of the road they're on and there's evidence posting a limit slightly below engineering recomendations is the safest.This is why 20mph limits work on side streets.
 

 The first video states quite clearly that system 2 is, or should be, put to work on streets, not roads (his definitions and let's not forget that he's talking America where streets/roads are generally wider). People are, or should be, more engaged.

The evidence from Penn State is all about roads, or appears to be as it is open to interpretation, with higher speed limits. And again, this is USA where street designs are much different from UK.

But fully agree with Charles Marohn, urban driving needs more engagement, 20mph zones are the most cost effective ways of reducing speeds, and it has been evidenced that this is working. Given more money, I suspect that we'd see more speed humps to literally kick that system 2 brain into action, more mini roundabouts, chicanes or whatever is required to slow the flow, but I suspect the stop start nature would be negative for the environment.

One of the things I like on the mainland is the random traffic light. If you exceed the speed limit on a straight piece of road with no junctions, crossings, nothing, a traffic light will turn to red thus taking the average journey time down. Exceeding the speed limit is rendered pointless.

I think both studies are relevent, The road through Roiget had 97% non-compliance with the 30mph limit and the council dropped it to 20 anyway, this caused the speeds to drop a bit, but also caused a big increase in speed variations and the non-compliance was then measured at 99.4%.
The road in question is also ribon devopment, meaning the road was there before the houses.

The problem with speed humps is that they cause pollution, damage to vehicles, and slow down ambulances. A better way is to design streets without traffic controls and low curbs, etc., that cause uncertainty in drivers' minds, leading people to naturally drive slower. They aren't aggrieved by it, and the traffic flows better.

I found Greek towns to be inspirational, back street intersections had no priority, no give way or stop signs and you drove straight through at your own risk... Or you stopped, looked and proceeded with caution.

Unfortunately the entitlement of english drivers ensures that they see these new fangled no kerbed roads as wider roads, that cheeky peds are allowed to use, but do offer safer parking as low profile tyres and diamond cut wheels are a nighmare (and expensive) on anything kerbed. And as you say the constant mounting and dismounting of kerbs in a taxi does indeed play havoc and damage vehicles. fortunately the horn exists to move these pesky peds out of the way, and as a courageous bus driver pointed out in his foul mouthed rant, something or other about getting out of his fucking way.

ajuk.uk [at] gmail.com wrote:

I think both studies are relevent, The road through Roiget had 97% non-compliance with the 30mph limit and the council dropped it to 20 anyway, this caused the speeds to drop a bit, but also caused a big increase in speed variations and the non-compliance was then measured at 99.4%.
The road in question is also ribon devopment, meaning the road was there before the houses.

I think this is only really a "question" where there's the cash and the will to completely rebuild the roads - which unfortunately there doesn't seem to be.  (Speed humps aren't free either and indeed lots more pricey than simply changing the signs - just a lot cheaper than a complete redesign).

When you say "non-compliance" - in one important sense that's quite irrelevant - that being "are people going slower"?  If they are ... then they are!  I agree keeping good tabs on the monitoring - so not just average but some measures of the variation - is important.

For me if 97% of people were already driving faster than the 30mph limit the fact that even more were driving faster than 20mph isn't really a biggie as long as they were (say on average) slower?

Quite often the road is there before the houses... that's development for you!  Question is - given that we've let people live there and places have grown, do we just say "tough - road was here first" or address that?

You're suggesting that compliance with the speed limit is irrelevant, as long as speeds decrease however there's also a chance that raising such an unrealistic limit would cause speeds to decrease.
There is such a prevailing myth that if you set the limit lower many or most people will only dare drive a set amount above the limit, in reality, when limits match the road, compliance is normally much higher, but speeds aren't. I think the average speed on that road was 32mph, that's more than 50% over the limit and that's the mean average, that's like setting the age of consent to 24 and calling people having sex below that age 'paedophiles'.
In the eyes of the law they are, but now being a paedophile is normal and socially acceptable because it no longer refers to people having sex with minors.
This is the absurdity of enforcing a rule that doesn't align with common behavior.
With a limit subjected to such levels of non-compliance you may as well not bother having a posted speed limit. But we need speed limits, they're important. My understanding of speed limits is that they're there to single out and target reckless drivers, if far too many people are exceeding the limit either the limit is wrong, or the design of the road is.

ajuk.uk [at] gmail.com wrote:

The problem with speed humps is that they cause pollution, damage to vehicles, and slow down ambulances. A better way is to design streets without traffic controls and low curbs, etc., that cause uncertainty in drivers' minds, leading people to naturally drive slower. They aren't aggrieved by it, and the traffic flows better.

Speed humps are not a great solution (they can be a literal pain in the arse for cyclists / difficult for adapted cycles etc.).  But they can help.

"Causes pollution".  Well ... I'm pretty clear that it's not the speed humps, nor speed limits, nor indeed cycle infra producing pollution.  It's people driving polluting vehicles that are really at the bottom of it, I'd say.  (Whether those are ICE vehicles or "emit some pollution elsewhere, but still particulates locally").  Yes - some people are going to drive like berks - even up to the point of damaging their own vehicles!  Depending on the fraction of berks that may steer us towards different ways of addressing that...

Ambulances?  I'm pretty sure the emergency services are consulted on most network changes including traffic calming schemes.  Not aware they're shouting about speed bumps per se?  I'm sure they would find some places proposed more or less appropriate depending on how they route across the network?

Your last part sounds like you're invoking an idea which has sometimes popped up under the "shared space" banner.  Removing some visual clutter / simplifying things can indeed be good.

However I think that we should do exactly the opposite overall to the "better behaviour through uncertainty" idea.  That's flawed - not least because sometimes humans just go nuts or do unexpectedly strange things when uncertain.  Per "Sustainable safety" it should be "better behaviour through always understanding what is expected" (predictability). 

I don't know if you're thinking of the whole "shared space" idea (e.g. doing this in a residential area) but that's widely recognised as being a bad idea for non-motorised road users and terrible for those with disabilities or sight impediments.

I should add - there are indeed some places in NL where there are fewer markings and even mixing of modes.  But those are e.g. residential areas where the narrowness of the roads, the fact these aren't through-routes (the UK seems to frequently default to "fully permeable for through traffic" layouts), the presence of trees and plants etc. should all provide notice that it's a place for people rather than just road for people driving.

But even there they had to first "tame the car" (or ... seriously reduce traffic volumes, change the driving culture and re-educate the drivers) before such spaces would work well and people would trust those driving.

The same author seems to show something that looks like a shared space in his peice about the 85th percentile speed. However rather than an fully shared space this shows lower curbs and bollards, not traffic calming per se. The issue with traffic calming is that it presupposes traffic is an inherently unruly entity necessitating continuous 'calming' measures.