The Toronto Transit Commission is somewhat different because its heavy rail lines use a combination of single-person and two-person crews. On the TTC's Line 1 and Line 2, trains operate with a crew of two train operators, consisting of a motorman and a conductor. The employees who perform these roles are crosstrained, and switch roles each time when a train reaches the end of a line and needs to reverse direction. The conductor is responsible for door control and observation and is located in the rear cab of the last car in a train. A trainlined buzzer system is used to notify the motorman that it is safe to proceed.