((a)) ** .—** This section applies, rather than section 21103 or 21104 of this title, to a train employee or signal employee during any period of time the employee is performing duties of a dispatching service employee.

((b)) ** .—** Except as provided in subsection (d) of this section, a dispatching service employee may not be required or allowed to remain or go on duty for more than—

((1)) a total of 9 hours during a 24-hour period in a tower, office, station, or place at which at least 2 shifts are employed; or

((2)) a total of 12 hours during a 24-hour period in a tower, office, station, or place at which only one shift is employed.

((c)) ** .—** Under subsection (b) of this section, time spent performing any other service for the railroad carrier during a 24-hour period in which the employee is on duty in a tower, office, station, or other place is time on duty in that tower, office, station, or place.

((d)) ** .—** When an emergency exists, a dispatching service employee may be allowed to remain or go on duty for not more than 4 additional hours during a period of 24 consecutive hours for not more than 3 days during a period of 7 consecutive days.