TWO MAIN TRACKS. The practice is still a novelty on the former British Rail, notes Where Worlds Collide. (Now imagine a 70 mph double-stack train going by your window three or four feet away, or, what's even more fun, catching up with one on the middle track.) The British are also discovering something that we learned here about 50 years ago, when it seemed like GP-7s were everywhere displacing everything, and for the same reason: they were reliable, and you could lash up enough to clean out just about anything the yardmaster could couple up. The English have yet to discover what happens when someone delivers a case of Armour Yellow paint.