<<<<<I believe that LT/LUL use a similar system in the London Underground.>>>>> I'd need proof! :-) O.S. Nock, a pom, wrote quite a bit on how NSW signalling was like nothing he'd seen, I would presume Nock would have been familiar with the signal systems in use by the London Underground. Mark. Visit my train pic website at: http://home.earthlink.net/~markbau/