Overtaking kills, so increase speed limits
You cannot overtake a car doing 70mph by doing 70mph, you are not supposed to be in the overtaking lanes unless you are overtaking. All vehicles can do 70mph now and they cannot fit all the vehicles into the left lane because there isn't the capacity. So two lanes of cars must be speeding, hence 80% of people speed BECAUSE THEY HAVE TO. Cut them some slack you micromanaging assholes.
Research in Texas showed that their increase in motorway speed limits from 55 mph to 75mph had NO effect on fatalities. It is not as clearcut as you think it is.
This study "Speed variance, enforcement, and the optimal speed limit Economics Letters, Volume 42, Issues 2-3, 1993, Pages 237-243 ",showed you get fewer accidents by harmonizing the speed of vehicles, and RAISING the speed limit was found to create smoother traffic flows than lowering them. (Can't link to it it's on Elsevier).
i.e. the risk of accidents occurs from slow vehicles mixing with fast vehicles, .... well duh, if every car travelled at the same speed in the same direction they could not hit! So putting cyclists and cars on the same roads is bad because there is a wide variance in speed. Bunching cars up in some sections is bad because where they bunch is a collision risk, and any phantom traffic jam that the bunching causes, also a collision risk before the road works.
30mph is not a magic safe number, that number came from misinterpreting a graph of the RATIO of fatal pedestrian-car crashes to all pedestrian-car crashes. In reality there was a huge *increase* of *non* fatal accidents below 30mph, which made the *ratio* of fatal to non fatal drop dramatically at 30mph, when in reality it does not. So the belief that dropping the speed to 30mph would magically make road works safe is not true*.
i.e. this graph is the one they use, but it misrepresents the data it was calculated from.
* If you're still not convinced, suppose there are 1000 accidents per million journeys that are non fatal and almost all are below 30 mph. i.e. faster roads like motorways are safer, but there are far more accidents on slower roads where pedestrians meet cars and these are nearly always non fatal.
Now suppose there is 1 fatality per million trips. And imagine if speed made NO DIFFERENCE at all. Whether 10mph or 1000mph, for this thought experiment, it's only 1 fatality per million trips.
Now calculate the same ratio Pasanen did for his graph. Notice that at 30mph there is a huge swing from fatal to non fatal accidents!.. So speed above 30 causes fatal accidents? But that cannot be, as I said 'imagine if speed had no effect on fatality' and we constructed the original data so that speed had no effect on fatality! Yet the derived graph shows speed has an effect on fatality!
So you see the problem with what Pasanen did, and nobody has checked that graph since to recognise the problem. They just quote and requote it in its different forms.
But the fix is better segregation of traffic from people and smoother traffic flows, and sometimes smoother may mean faster!