To be clear, I'm not saying that the goal of reducing speeds is bad. I'm just saying that attempting to do so on the cheap by changing the rules instead of the built environment itself accomplishes nothing but to generate more lawbreaking. Well, that and potentially making the road even less safe than it was before because having a wider mix of speeds is even worse than having everybody at a uniformly too-high speed.

Absolutely right. My town just made every road 25mph. Great. Unfortunately nobody gives a fuck. The road out in front of my house just got repaved. It's beautiful. I love it. Pulling in and out of my driveway has never been better. People also blast down it, mainly because I think they perceive speed differently on a nice smooth tarmac versus what was a cratered surface rivaling the moon. My suggestion to my neighbors is we just keep cars parked on the street all the time. If folks in opposing directions need to stick to a side to let others pass, it will naturally cause them to move more slowly.

Edit - Forgot to add, I listen to traffic engineers testify pretty regularly and consistently get mistreated, so I just want you to know that I appreciate what you're saying and what you do.

Step 1: reduce speed limit
Step 2: always have speed trap in place
Step 3: profit

I largely agree with you, but I also recently saw this article: https://www.euronews.com/next/2023/07/26/inventive-or-stupid-french-village-disorients-drivers-with-crisscrossed-white-lines

A lot of these changes are coming in the wrong order - first you improve public transport, create affordable housing near city centers, and drastically reduce the price (and let’s be frank, increase the quality of) public transport, and THEN you hit car users to push them on to these options. In the current order, they just introduce further hardship to folks who already have a bad time.

It might be a little different in the UK, but in North America step #1 needs to be "first you abolish the low-density zoning restrictions that displace almost everybody far away from the city center to begin with." It's not just that walkable housing isn't affordable; it's that it's not even allowed by law to exist.

Yeah, the current approach globally - at least it seems to be the same in Germany - is to make the "experience", if you want to call it that, for car users worse to the point that it's worse than public transport in order to force people onto it. There are some minor improvements being made to public transport, but it's of course a lot faster to put up signs for a speedlimit everywhere or even blocking access to certain roads completely than to increase the capacity of a rail network. And as you said, this hits the already disadvantaged parts of the population more, since they more often than not have manual labor type job that requires going into the "office" everyday, that are living further from work, ...

Missed one - you actively encourage mobile working so you have less people moving around in total.

Purely anecdotally, the vast majority of my collisions have been at very low speeds - in parking lots.

The fact that you talk like you have enough samples to make that inference worries me.

1. Why will every driver go over 20mph/30kph? Are they incapable of maintaining that speed? All school and community zones in my country are 30kph; are we wasting our time with those?

2. I'm a vision zero proponent, so I don't care about the number of collisions; I care about the number of fatal collisions first, serious injuries second, minor injuries third. So even if 20 mph maintains, or even increases collisions; so long as it reduces casualties, it's positive. Bumpers are replaceable; people are not. The AAA document you link even says a 10% reduction in mean speed reduces fatal crashes by ~34% in the executive summary.

My main concern with this is that what you're doing is desensitising people from the speed limit.

I'm from a country that has arbitrarily defined speed limits and VERY low compliance rates compared to the UK (if you've ever been to Italy for example you know what I'm talking about). The nice thing here is that because the vast majority of roads have a speed limit that 'feels' appropriate (ie the road is designed for its speed limit), the amount of speeding I see here is negligible compared to what I was used to.

And generally here when the limit changes people comply to it because you can trust there's usually a good reason.

There's roads near me that are arbitrarily set to 30 (no pedestrian walkways, no side roads, but it passes near the back of houses and I assume they successfully petitioned the local authority to change it to 30), and traffic flow there is usually 40-45. I've never seen an accident there.

We have a poorly designed intersection not too far away and there's always accidents there to the point that there's now a consultation to fix it.

If this rule came to England, both these roads would be turned to 20, and that won't really be solving anything. In the first example I assume locals will still be driving 40, and it will create unnecessary overtaking because the road is wide and the visibility is good so it's not necessarily unsafe. But you've gone from a safe 40 road to risking head-on collisions pointlessly.

We have this speed limit in the Netherlands, mostly in areas with housing. It doesn't really affect busses because they stay on the bigger roads that are 50 kmh (about 31 mph). In my opinion it's fine to drive 20 mph on the more local roads, as long as there are collector roads where you can go a bit faster.