A guard was accidentally stranded at a railway station when the train left without him.
Passengers had to get out through the driver's cab door at the next stop and were delayed for an hour waiting for another train.
The conductor on the 08:16 Ilkley to Leeds service was left behind at Burley-in-Wharfedale station. The train and its passengers stopped at Menston.
Northern Rail said it was an "operating incident".
Passenger Simon Painter said: "We were offloaded on to the platform via the driver's cab and then waited at Menston for the next train.
"Left Ilkley at quarter past 8 and arrived Leeds at twenty to 10."
A spokesman for Northern Rail said: "Shortly after 8.23am on Tuesday 31 January the 8.16am Ilkley to Leeds service was delayed after the train left Burley in Wharfedale station whilst the conductor was still on the platform.
"As a result, the service was terminated at Menston station."
"We are currently investigating the cause of the incident and it would be inappropriate to comment further until that investigation has taken place."
The incident led to delays on several other services between Ilkley, Bradford and Leeds on Tuesday morning.