Some companies require that these tests be passed within the first few years of employment. Until permanent positions become available, new conductors are put on the extra board, where they substitute for experienced conductors who are absent. On most railroads, conductors on the extra board may work as brake operators if there are not enough conductor runs available for them that month. Seniority usually is the main factor in determining promotion from brake operator to conductor and from the extra board to a permanent position. Advancement to conductor jobs is limited because there are many more brake operators than conductors.
Most railroads maintain separate seniority lists for road service and yard service conductors.
Conductors usually remain in one type of service for their entire career. On some railroads, however, conductors start in the yards, then move to freight service, and finally to passenger service. Some conductors advance to managerial or administrative positions. For subway operator jobs, subway transit systems prefer applicants to have a high school education. Some systems require subway operators to work as busdrivers for a specified period of time.