Nice one! When flying from RAF Boulmer a few years back, with the main line very close to the base, it occurred to me to think about how best to warn a train driver of an obstruction on a level crossing; all I could come up with was to deploy the winchman with a signal pistol beside the track a mile or so one side of the problem, then take the aircraft the other side of the blockage and use landing lights/smoke grenades to attract the driver's attention. Trouble was that if the aircraft was heavy, or there was even a slight headwind, the Sea King was actually slower than the express trains so time might have been extremely tight!