What I see is definitely more dangerous. Cars stack up in the passing lane behind the passing truck. Impatient people then jump into the empty slow lane to pass the line of cars on the right, then merge greedily cutting in front of the line, making the whole situation worse.

So drop the limit to 60 for everyone?

Low limit for everyone leads to more accidents - drivers watch speed and try to race between speedcameras instead of riding through quickly but safely.

Right: even with current limits, I spend a completely unreasonable amount of time glancing at the speedo, worrying about if I'm going over the limit and trying to shepherd the speed within the limit, rather than paying more attention to the traffic conditions around me. This is actually much worse on 20 roads that are converted from 30s by just swapping the signs: they were specifically designed for higher speed, so it's a constant, conscious effort to keep the speedo in mind and sight and carefully not drive to the road.

I feel that this is something people didn't have to do so much: with an analogue speedo, you can't really see your speed to 2 sig figs while driving, with a digital one, you know if you're at 20 or 23 (after your car speedo error, obviously). The implication is that it previously wasn't so important to drivers.

Unlikely. I think 10%+ changes in speed are much more dangerous than a 1% higher speed overall.

Dense traffic is less safe than loose traffic. Having a dense traffic flow behind the blockage is going to negate any wishful thinking improvement you get by reducing traffic speed by 10%.

> Dense traffic is less safe than loose traffic.

It's not that simple. According to [1] the relationship is U-shaped, with the least accidents per million miles driven occurring at about 1500 vehicles per hour. Less traffic increased accidents number, more traffic decreased accidents number but increased average number of cars in each accident. The sweet spot was in the middle.

Additionally after a certain traffic threshold accidents stop being deadly (because of slow speed).

But the results varied depending on road types, countries, time resolution of data and weather conditions.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6766193/

I don't think the reduction in speed from 70 to 60 is as significant as bunching cars from 10+ seconds gap to 2, or less for BMWs.

Breaking distance and collision energy scale with square of the speed. So reduction from 70 to 60 is 27% reduction.

Also minimal safe distance is 3 seconds at your current speed. If you can't keep that distance because of traffic - you should slow way down, not to 60 km/h but much lower. So either your comparison isn't fair or the person doing 60 km/h with 2 seconds of gap is the reason the road is unsafe, not the traffic.

Two seconds is a very standard rule of thumb. https://en.m.wikipedia.org/wiki/Two-second_rule

And if you've ever actually encountered a queue behind a slow vehicle, you'll know that leaving too much of a gap will cause undertaking luxury German cars to magnetically be sucked into it (no fault if their drivers of course, its all done in the engine control software I hear), suddenly leaving you with 1 second of gap, until you can ease off and grow the gap gently without having the car behind you pile into your rear end.

Either way, the separation in free traffic is hugely greater than in any queue.