Four people were injured when two engineering trains crashed near Bristol on Wednesday.
The collision, in the Acton Turville area, closed the line between Swindon and Bristol Parkway until around 1500 GMT, leading to some delays.
Two rail staff who were hurt remain in hospital and 50 homes near the crash site were evacuated to allow giant cranes to lift the wreckage.
An investigation is under way to find the cause of the collision.
Trains between Swindon and South Wales were being delayed by up to half an hour - with trains being re-routed through Bath Spa.
Ben Herbert from Network Rail said the collision was on a stretch of line closed to passengers.
"The area was closed for track renewal - we're replacing sleepers and the ballast - the gravel under the tracks," he said.
"The trains are used by engineers to carry out work. We've evacuated the nearby houses purely as a precaution while the trains are lifted off the tracks."