But driving at 70 on a busy motorway is quite difficult - the slow lane is full of trucks crawling along at 55-60 and both other lanes tend to move along at 80 or so. Going at 70 in the middle lane leaves you open to being cast as one of those annoying middle lane hoggers, so I tend to end up having to keep changing lanes, which is surely more dangerous...
For example, the latest official statistics[1] in fact say that "On motorways in 2008, 49 per cent of cars exceeded the 70 mph speed limit. In addition, 15 per cent of cars were recorded as travelling at 80 mph or faster."
While nearly 7 in 10 drivers exceeded 30mph limits ten years earlier, just under half do so now. These roads and motorways are by far the most common road types for speeding.
In other words, your "the majority speed" claim and your claim of the 85% level are both some way off.
[1] http://www.dft.gov.uk/pgr/statistics/datatablespublications/...
http://www.abd.org.uk/motorwayspeedlimit.htm
"On motorways in the UK, the 85th percentile speed for cars is approximately 85 mph, i.e. 15 mph above the current limit."
"speed surveys show that 56% of car drivers exceed the 70 mph limit on motorways in this country and a significant proportion regard 80-85 mph as a normal cruising speed."
Don't get me wrong, I think that 30mph limits should mean 30 - as long as they are placed as they should be - But motorway driving is completely different. Driving 80 or 90 on a motorway when there is no real risk should not be a crime IMHO. Cars are safer and the vast majority of car accidents happen on smaller roads at slow speeds.
Having speed cameras on motorways is just an alternative to toll booths.