Addition to above:

12 Hours maximum on duty time provided previous off duty time meets or exceeds minimum (8 or 10 hours off).

1 minute to 11 hours 59 minutes on duty requires 8 hours off to work another 12; or time may be "split" by a respite.

12 hours on duty requires 10 hours off duty.

12 hours, 1 minute OR more time on duty requires 10 hours off duty and results in an Hours Of Service violation. Employees may be ordered by a supervisor to violate the 12 hour limit during an "emergency", which may result in the railroad company getting fined for the violation.

The 12 hour maximum may be "split" by a respite of **4 hours UP TO 7 hours and 59 minutes** off duty.

Once the minimum off duty time is met (either 8 or 10 hours off), and employees may work another 12 hours.

Example: 6 hours ON duty, 7 hours 59 minutes "respite" OFF duty, another 6 hours ON duty equals 12 hours ON duty, but with an elapsed time of 19 hours and 59 minutes.

There are many complicated situations that are addressed by the Hours Of Service rules, such as called and released before and after reporting for work, commingled service, deadheading, limbo time, et cetera.