> The Elizabeth line (it was called Cross Rail during development) is the first train line that combines both the national rail infrastructure and the London Un

> The Elizabeth line (it was called Cross Rail during development) is the first train line that combines both the national rail infrastructure and the London Underground. Combining the signalling systems has be an incredible complex problem. No, it isn't. Historically the boundary between the Underground and the rest of the "mainline" railway network used to be even fuzzier with lots of through-running, but even today a few stretches of lines served by both Underground and mainline trains remain (the Metropolitan Line north of Harrow-on-the-Hill, the outer ends of the District Line to both Richmond and Wimbledon, the Bakerloo Line north of Queen's Park). What's true though is that due to its capacity requirements, Crossrail is using a different signalling system than the rest of the railway network, which means lovely interface issues at the transition points…