How do the drivers in the leading loco(s) and the banker(s) communicate?
These days, it is more common for crew to be issued walkie-talkies, so communication is a bit less of a problem, but without them, coordinating the banking efforts with the leading loco always called for great skill and ingenuity. The drivers made use of horn signals, brakes, and also closely observed the load on the locomotives (by monitoring the traction motor currents, engine rpm, etc.). With all this, the drivers ensure that the leading loco does not handle too big a load (putting the couplers under strain), nor do the bankers handle too much of the load (working against the leading loco). In steam days it was even harder, as there was no convenient gauge corresponding to the motor current or other meters in modern locos that allow judging the load. Then, all communication was through the whistles, monitoring the vacuum in the brake pipe, and monitoring the steam intake and ‘listening’ to the loco!
