The UK Department for Transport estimated that cameras had led to a 22% reduction in personal injury collisions and 42% fewer people being killed or seriously injured at camera sites. The British Medical Journal recently reported that speed cameras were effective at reducing accidents and injuries in their vicinity and recommended wider deployment. An LSE study in 2017 found that “adding another 1,000 cameras to British roads could save up to 190 lives annually, reduce up to 1,130 collisions and mitigate 330 serious injuries.”

"Enforcing speed limits in areas that matter leads to better compliance in those areas and a reduction in deaths"

That doesn't mean we should reduce speed limits everywhere, just that we need to enforce safety where it matters.

“Our research suggests the growing use of average speed cameras in motorway roadworks and increasingly on sections of A-road is reinforcing the road safety message as they are extremely effective at slowing down drivers. … “For instance, on the A9 in Scotland the number of deaths has halved since average speed cameras were introduced between Dunblane and Inverness in October 2014.

Mate, the A9 is a beast in and of itself. It's the one road that connects mainland Scotland (Glasgow & Edinburgh) with the rest of the country, if you exclude Aberdeen. When the A9 has a major accident (which happens far too frequently) then you often have to detour 50 miles, easily more if you don't pick the right route first time.

The A9 single carriageway average speed cameras are pretty reasonable, though, more or less. What would be more reasonable would be dualling it all the way, or at least dualling the key accident hot spots, the bottlenecks. Then if they had a crash they could divert to the other carriageway, rather than queueing up traffic for half a day and expecting people to turn around and navigate across the lower highlands.

Suffice it to say, horses for courses. We can have speed regulation and enforcement where it matters, and we can have national speed limits that leave drivers to driver to the conditions. All of these measures of changing the rules are nothing but bullshit though, not when we have no formal system of teaching the new rules to existing drivers.

Ongoing training for drivers is needed. Not necessarily ongoing pass/fail tests, but at least a CBT course every couple years, to brush up on the latest rules if nothing else. This avenue would offer far better safety improvement than anything else.

Interesting, that's the first I've heard of it - at least, aside from temporary 20 zones around schools and the like. I think most forces are avoiding 20 limits because it's legally not that well tested, there's a slightly higher potential for someone to come up with a novel defense. I guess that doesn't stop revenue coming in from people who just take the fines without challenging them.

Could you please tell me, which country are you in? England/Wales/Scotland.

These reductions in speed limits are primarily political, while corruptly funneling money to overpriced contractors and police running deceptive speed traps.

I'm talking generally about speed limit reductions here. Not just 30 to 20, but 60 to 50, 40 to 50 or 40 to 30. Sometimes it's done with valid safety intentions, backed up by data. More often than not it's done as part of some bullshit political project.

From another of my comments:

The limits are assigned so politicians can pat themselves on the back and maybe score some votes. Sometimes also so some new speed trap locations can be created, catching people out in areas where the road feels like it has a higher speed limit (although this is perhaps less true for 20 zones).

I'm not aware of police extensively enforcing 20 zones, but I am aware of police enforcing speed limits in areas where it has been reduced for arbitrary reasons. Quite often these involve civil works that are ludicrously overpriced and under-delivered, which reeks of corruption.