;NR:Network Rail
;NRM:National Railway Museum
;ORR:Office of Rail and Road, formerly Office of Rail Regulation, the independent safety and economic regulator for Britain's railways which includes HM Railway Inspectorate;OTMR:On-Train Monitoring Recorder, a device similar in principle to the flight data recorder found on aircraft.
;OW&W
;OWW:Oxford Worcester and Wolverhampton Railway