(a) Except as stated in paragraph (b) of this section, each relay that affects the proper functioning of a crossing warning system shall be tested at least once every four years.(b)(1) Alternating current vane type relays, direct current polar type relays, and relays with soft iron magnetic structure shall be tested at least once every two years.(2) Alternating current centrifugal type relays shall be tested at least once every 12 months.(c) Testing of relays requiring testing on four year intervals shall be completed in accordance with the following schedule:(1) Not less than 50% by the end of calendar year 1996;(2) Not less than a total of 75% by the end of calendar year 1997; and(3) One hundred percent by the end of calendar year 1998.(d) Testing of relays requiring testing on two year intervals shall be completed by the end of calendar year 1996.