Commuters in Hertfordshire faced long delays on Tuesday morning after a freight train derailed near Hitchin station.
A wagon came off the tracks in a yard adjacent to the station.
According to Network Rail, it damaged signalling equipment which meant passenger services were disrupted.
They tweeted: "The freight derailment in a yard at Hitchin cut the cable controlling a set of points on 1 track through the station.
"It’s not a difficult fix so we hope it will be repaired soon and will update when we have more."
Thameslink and Great Northern services during Tuesday's rush hour were affected, with long queues building up outside the station.
According to Mark Dack, a passenger held up by the disruption, his train had to move very slowly into the station because of the derailment.
Train operator Great Northern said on Twitter that the train, operated by another company, had derailed at low speed within the "depot/sidings" at Hitchin station.
Sharing photos of a derailed freight train car with some of its wheels off the tracks, Great Northern said in a tweet that Network Rail had teams on site working to fix the issue.
The National Rail Enquiries website said the incident meant trains were unable to use platform one at Hitchin station.
Services from King's Cross to King's Lynn were running between Cambridge and King's Lynn only, while Hitchin had a reduced service towards London.
Earlier, travellers were being warned of cancellations and delays from Cambridge and Peterborough towards London, with journey times extended by up to 60 minutes.
Tickets were being accepted on alternative routes run by Thameslink, Greater Anglia, Cross Country, LNER and East Midlands Railway as well as on local bus routes.
Shortly after 9am, a Network Rail Twitter account said workers had fixed a cable, cut by the derailment, which controlled a set of points on one track through Hitchin station.
National Rail Enquiries subsequently said services were returning to normal, but disruption was still expected to last until 12.30pm.
A spokesman for Great Northern said the freight train was operated by DB Cargo.
The disruption ended at around 12:30pm (Tuesday) with services getting back to normal.