I still dont agree that we need a 70 or more speed limit. I do 40 miles a day motorway driving and do a steady 55 ish, and still see the same cars that pass me at high speed early on in the trip, normally just before I leave the motorway, so dont see the point when a mile down the road an artic holds them up while overtaking another artic at nearly no speed difference. And I also say speed does kill, the same drivers that misjudge at 70 would have more time to correct at 50 with the same distance involved. So other than just being a bad driver, going too fast in a given circumstance is a large part of accidents.
We will have to partly disagree but lets not argue on this point.
Here's my view.
The speed on the motorway doesn't really make a great deal of difference to safety. The motorways are the safest roads on the country. You can do whatever speed you like but I will drive at the speed most appropriate to the conditions. That means that sometimes I will drive faster then your steadfast 55mph and sometimes I will drive slower. The speed showing on my dash is just to keep me legal, the speed I travel at has to fit the conditions for safety.
Speed doesn't kill.
Andy Green drove at 760mph and no one was killed or injured.
Millions of people travel at many hundreds of miles per hour and yet I've yet to see a trans Atlantic plane run over a child.
I do see news stories of parents running over their own kids on their driveway at less then 5mph.
Speed is a relative thing and needs to be appropriate to the prevailing conditions.
70mph, or even 80mph, is safe on a clear motorway, in good weather with good visibilty on a well maintained vehicle.
5mph is dangerous on a driveway when your kids are playing around the wheels of the car!
A driver who can't judge safety at 70mph should not be driving. Reducing the speed to 50mph wouldn't make the driver any safer as he/she would just drive closer, still not slow down in poor conditions nor adapt their driving anymore then they did at 70mph.
As you say 'Going too fast in a given circumstance is a large part of accidents.' is very true. The key point is 'going too fast for a given circumstance'. 50mph is too fast in some circumstances, as is 30mph and 20mph and 5mph.
The missing ingredient is drivers being able to make that distinction and many can't.
So saying 'I will do 55 as it is safer then 70' is a fallacy.
Driving at a
safe speed, up to the maximum legal speed, in the given conditions would be better.
Then there is also the 'making good progress' part to consider.
Being unable to make good progress along with other road users can also be a problem. Driving excessivly slowly can be a danger in some conditions and in those cases perhaps the driver shouldn't be making that journey by car.
I know people who refuse to drive more then 40mph, even on motorways, but they also seem to refuse to drive any slower then 40mph on urban roads.