In a 'past life' I've had to get train crews to some very odd locations. e.g. if a train has just struck and killed somebody, a new driver has to be sent out to take over the controls. (There's an automatic assumption that the original driver wouldn't be in a fit state to carry on working). So I've had to explain to a taxi controller that I need a car to to take a driver to a train which is in the middle of a field, in the middle of nowhere, and I've no idea of the access route to get to it anyway!
The company I worked for stabled all of its trains close to the two signing-on points (at large railway stations) used by members of train crew, so drivers and conductors simply turned up at the relevant stations and either boarded the trains there or walked a short distance to the local depot.
Other companies will have a signing-on point (possibly in a Portakabin or similar), together with staff car parking, close to the sidings where trains are stabled. Otherwise they might have a minibus to take train crews from their signing-on points to trains.
Train crews (particularly drivers) can still end up stranded though. I've taken a phone call from a freight company (EWS), whose driver had been booked to do a late-night run to Sizewell Power Station (to collect nuclear waste), only to find that the job had been cancelled. So he'd ended up in a signal box, in a remote part of Suffolk (where all the taxi offices close at 6pm) and, even though I worked for a completely different company, it was still my job to find a way to get him back to his home in Peterborough!
Oh, happy days!
;-)