MBTA officials said regular service has resumed after a slow speed derailment on the Haverhill commuter rail line on Monday morning.
The derailment happened near the Ballardvale station in Andover, causing delays of at least an hour in some cases.
For several hours, the Haverhill commuter rail line was bused between the Ballardville and Reading stations to connect to train service.
Full train service resumed around 3 p.m. after tracks and switches were inspected. Minor delays of 10 to 15 minutes should still be expected.
The MBTA said a preliminary analysis showed that the switch was not properly in line at the time of the incident. The precise cause is still under investigation but is believed to be human error.
Hundreds of people were standing on an MBTA commuter rail platform when Sky Ranger arrived over the scene on Monday morning.
MBTA officials tweeted out photos showing crews efforting repairs. One photo showed the train's wheels spanning two tracks.