I wonder how many lives could be saved by an efficient and affordable rail network?
However, I don't think everyone believes the limits are there for a good reason. Actual quote I once heard: "they're just playing silly buggers in their control room, ain't they, they don't know anything". Not helped by many other signs crying wolf about obstructions that often aren't there at all.
As for all-lane-running, casual observation of UK driving indicates to me that a blitz on driving standards[1] such as "keep left", "avoid making others brake" and "when you change lane or merge, it's your job to match your speed to the new lane"[2] would be a far quicker way to increase capacity and reduce accidents. And would cost substantially less than the billions spent on smart motorways.
[1]: especially as motorway driving isn't on the driving test and learners weren't allowed on motorways at all until 2018, so most drivers have never had any formal motorway training.
[2]: Not only cars: I see HGVs doing 58 diving into gaps in 70mph traffic (on two lane roads especially) and causing half a mile of brake lights and converting free flowing traffic into nose-to-tail queues every day.
The geography of the UK makes it difficult to require that- there are very large areas where it wouldn't be possible for a learner to reach a motorway then get home in a typical 2 hour lesson. Even if you only required learners to go on a national speed limit dual carriageway it wouldn't be possible in some places (far north of Scotland, for instance).
A few weeks back I had a journey on the M42 at evening rush hour where the dynamic speed limit was frequently cycling between NSL -> 60 -> 50 -> 40 -> NSL. Each limit was enforced for 1-2 gantries.
Even to someone who understands the benefit of dynamic speed limits for ensuring good traffic flow, it's not a good experience.
[0] https://en.wikipedia.org/wiki/Motorway_Incident_Detection_an...
There's supposed to be an End or a national speed limit sign, but there wasn't.
That's the theory. However, based on my experiences, it seems the control loop is badly tuned. In general, people's paniced response to a new speed limit needs turning down. All that happens is that people randomly slow down or brake at each new speed limit, and 1/2 mile down the road, there's the regular traffic jam anyway.
I'm thinking specifically about the communication around the plan to automatically shut down a lane when a car breaks down in that lane. They cited the time it would take their control center to detect the lane would need to be shutdown as the time it would take to render the lane safe. This ignores that all the cars also have to stop, which takes time.
People have been killed in traffic accidents on smart motorways because there has been no hard shoulder available. On the other hand, smart motorways save lives because they reduce congestion - and the calculation is that more people are saved by the lack of congestion than are killed by the lack of a hard shoulder.
The problem is that you can show the faces of the people killed on smart motorways due to lack of a hard shoulder, but the people who weren't in fatal accidents will always be faceless.