Train operators are continually cautioned that, if they have to hook down the automatic stop arm in order to pass an automatic signal, they must release the stop arm again immediately after the train has passed, unless okayed by the signal maintainer or other qualified employee. The MAIN reason for releasing the stop again is:
a. to give protection to a following train
b. to signal the end of the route
c. to conserve energy
d. to adjust the braking system