Some companies require these tests to be passed within the first 2 years of employment. New conductors are put on the extra board where they substitute for experienced conductors who are absent, because of vacation, illness, or other personal reasons, until permanent positions become available. On most railroads, conductors on the extra board may work as brake operators if there are not enough conductor runs available that month. Seniority usually is the main factor in determining promotion from brake operator to conductor and from extra board to a permanent position. There is a great deal of competition for conductor positions because they are fewer in number than entry-level occupations.
Most railroads maintain separate seniority lists for road service and yard service conductors.
On some railroads, conductors start in the yards, then move to freight service, and finally to passenger service. Some conductors advance to managerial or administrative positions. Extra board designees work only when the railroad needs substitutes for regular workers who are absent. Extra board workers frequently must wait years until they accumulate enough seniority to get a regular assignment. Seniority rules may also allow workers with greater seniority to select their type of assignment.