RULE 251-D. The January 2003 issue of Trains features the end of double track operation on the Santa Fe lines in Arizona and New Mexico. Those lines were distinctive in North America as trains operated left-handed (so as to take advantage of favorable gradients further west), requiring gantry signals in order for the engineer to be able to see the signal without a steam locomotive boiler getting in the way. "Probably no other railroad, save the Chicago & North Western, had as many route miles operating left-handed." That would be in North America: Santa Fe's left-hand running is about 453 miles of track, whilst Paddington to Penzance is 305 miles of double track operation, excluding the Royal Albert Bridge.

The Arizona and New Mexico lines are now dispatched by Centralized Traffic Control, and the discipline of taking siding to clear an overtaking superior train's schedule has passed (as have the cabooses that made lining the track easier.) There is a sidebar in the Trains article on how it worked: entirely by use of outside sidings and exit signals circuited to the third block in the rear. No reason to have a block operator awaiting 1-5-5 from the signalman in rear. It gets rather chilly on the Colorado Plateau.