If it goes wrong you'll find running into someone on a motorway at 90 hurts hust as much as it would on a courty road or resofential side street. Physics doesn't discriminate.
Well, of course the
severity of a crash at 90 mph is higher than at 70 mph, but risk profile is a function of both severity and likelyhood. You could just as well argue for motorways to have a 50 mph speed limit, or 30 mph, or... yes, I know, reductio ad absurdum.
But talking of the absurd, and risk profiles, time trialling on a 70 mph dual carriageway.
The severity of a crash is very high - but at quiet times, the likelyhood of a collision is low. If you wanted zero risk, you'd never leave the house... except that most accidents happen in the home!
Now for the absurd part, the above is an
all purpose road with the same speed limit as a motorway ffs! Yes, I know, the speed limit for HGVs is theoretically different by 10 mph, but we all know that Joe Trucker is sat pressed against the 52 mph limiter having a "pleasant" time with his laptop on both kinds of roads.
Frankly, I'd much rather be passed at 120 mph by someone who gives a full lane change, than at 70 mph "I wasn't speeding guv" trying to occupy the same bit of road as me. In fact, if driving standards were perfect, would not speed limits be completely unnecessary, as everyone would drive an appropriate speed for the conditions?
I'd rather see the morons kept off the road, than the "oh, morons keep crashing off this corner, so we'd better put in a 50 mph speed limit to slow them down". Which works nicely, until there's a cyclist around the bend. I'd personally prefer that they hit the tree on that previous bend...