"Earl Purple" wrote in message
ups.com...
And actually, a road, if used properly, will usually take a greater
volume than a railway. On a D2 dual carriageway, for example, if cars
are travelling at a 2-second gap,

This assumes that all cars will leave this gap at all times. I try to
maintain a 100-150yd gap in front at all times, and more when travelling at
very high speeds.