dennis@home wrote:
"The Natural Philosopher" wrote in message
...

Its 20% off journey times directly, but more imnportant it would reduce
congestion. Unless you think that congestion is actually keeping the vast
majority of drivers off the road, and clearer roads would simply attract
more traffic..

The capacity of a road goes down as traffic gets faster.
Unless its full of idiots that don't keep a safe distance.



No it doesn't. Cars per hour is similar, but since they are all going
faster, they all take less time to get there. Overall you get more
journey miles per hour at higher speeds.

A simple *reductio ad absurdum* shows this to be the case.
Consider: A suite of cars dong 1 mph over a stretch of single
carriageway road that is say 100 miles long.

Well put them bumper to bumper - say 12 feet apart.
So at any given time we have 100 miles x 5280/12 cars on the road.
Thats 44,000 cars all doing 1mph, so the total car miles per day is
44,000 * 24. That is a shade over a million car miles a day on that road.

Now put them on at 100 miles and hour, and space them ten car lengths -
so its 4,400 cars on the road, and they are doing 4,400*100*24 car miles
per day. A shade over 10 million car miles per day.

10 times the snails pace where they are squeezed as tight as they can go.

Or let's stop them all..thats as slow a speed as you can get. That's
zero car miles a day. Great.

Never mind the beneficial aspects of low journey times on drivers stress
levels and alertness..

The reality of this is why you get compression waves in car congestion.
The flow, once interrupted, slows to a halt because once below cruising
sped, the road cannot handle the car numbers. One slow car pulling out
of a junction onto the M25 causes an accident 20 minutes later and 20
miles further back on the motorway.