Rail passengers faced a day of disruption after a tractor rolled down an embankment onto the track near Golspie in Sutherland.
Services were disrupted between Inverness and Wick after the incident at around 7am.
Passengers faced lengthy delays on the route, with Scotrail running a replacement bus service between Tain and Brora, stopping at each station in between on the affected lines, adding up to four hours to journeys on the route.
A spokesman for British Transport Police said it was unclear how the tractor had ended up on the lines near Dunrobin Castle, north of Golspie.
The spokesman said that an investigation is ongoing into the incident.
The tractor was not removed until around 2pm today after police carried out an investigation at the scene.
A spokesman for Network Rail said: “Our engineers looked at the line after the tractor had been removed and it became clear that there was damage to sleepers and the track itself.
“These were repaired before it was safe to run trains on the line again.”
