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Rail disruption hit the network for more than 24 hours, with the line blocked between Hereford and Shrewsbury, after the crash.
British Transport Police arrested a 32-year-old man who was released under investigation.
Two of the people who were injured were taken to hospital and later discharged.
Those on board described a "really loud bang" as the train hit the trailer, leaving "debris everywhere".
The level crossing takes a farm track across the railway lines and is only used by agricultural vehicles.