The company's major income-earning sources are its rock trains, transporting primarily limestone, and intermodal trains. FEC freight trains operate on precise schedules. Trains are not held for missed connections or late loadings. Most of the trains are paired so that they leave simultaneously from their starting points and meet halfway through the run and swap crews, so they are back home at the end of their runs. The FEC pioneered operation with 2 man crews with no crew districts, which they were able to start doing after the 1963 strike. The entire railroad adopted positive train control (PTC) after a fatal 1987 collision caused by a crew not obeying signaling. (PTC is a safety feature long-sought by federal safety officials for all railroads).