Your friend sounds like a tit and you sound quite old.
I don't think you are coming across very well on the forum, but then I'm new, perhaps this is normal and accepted behaviour. If it is, might be the wrong place for me to hang out or post.
The previous guy said, if everyone drove at 60 we would all get there quicker. Actually if everyone drove to the speed limit we would all get there quicker.
That's incorrect, presumably you have not seen any research on the subject. As traffic builds up speeds have to drop, at a certain density it then doesn't matter you can't prevent the shockwave jams. Plus a high proportion of people follow to close. At high speeds, these shockwaves come at much lower densities.
You don't get there very much faster, and you cause delays for everyone else. I have never had a situation where I can travel at a constant 70 on the motorway for more than a few minutes. Lane discipline is bad, drivers follow too close and pretty soon you will have to brake, then speed up again then brake, time and time again. this causes problems.
This is just one aspect of it and why we have variable speed limits on many motorways especially the M25 and now average speed cameras as well as the M25 idea first implemented made it worse as drivers slowed down under gantries and then speed up again, slowing down just before the next camera!
The unified map for automakers and enterprises.
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You can see the shockwaves in simplified form here
If you add to the equation: more accidents, less safety safety, wear and tear, fuel economy, lane discipline, bad driving habits and lack of anticipation...shooting along at 70 in most instances is a mugs game. You may be a superior driver, but a high % of people are not.
Believe it or not I was a driving instructor for a period in London, covering from Hampstead to Putney. So I had to learn a bit of theory.