 Train cars were numbered 1 to 5 with 1 and 5 being "cab" cars.To keep operations consistent, when the sixth car was added, the additional car was designated car "3A" (rather than 4 making the back end Car/Cab 6); that way pilot operations from the rear cab retained the "Cab 5" designation for all trains regardless of size (this practice continued until the Mark VI trains had fully replaced the Mark IVs at which time reverse motion was conducted as "Cab 6 Operation").Car 3A did not include engines.