Federal transportation safety regulators have determined that a Norfolk Southern locomotive engineer was responsible for causing a derailment in Easton, Pennsylvania, last year that involved three trains.

The National Transportation Safety Board said the engineer failed to follow restricted speed requirements.

However, the NTSB report also cited lack of positive train control safeguards that could have provided protection against human error.

The derailment began when intermodal train 268 rear-ended stationary intermodal train 24X on Track 2 of the Lehigh Line.

Three of 268’s cars derailed and fouled adjacent track 1. Just over a minute later, westbound NS manifest freight 19G struck the derailed equipment.

Six cars on the 19G and its two locomotives derailed. The locomotives were partly submerged in the adjacent Lehigh River and leaked diesel fuel. Four crew members were treated for minor injuries.

The 268 was operating in the same signal block as the 24X, which had stopped at a red signal at a control point due to traffic ahead. Train 268 passed an automatic signal which indicated that the train could proceed at restricted speed, which the NTSB report said is defined as no faster than 20 mph or slow enough to allow the engineer to stop a train within one-half the range of vision.

In an interview with investigators, the engineer of the 268 said he knew the rear of the 24X was in the signal block that his train was entering and assumed it was continuing to move.

The incident occurred in an area of limited visibility due to elevated terrain and vegetation along the curved tracks that parallel the Lehigh River.

The engineer of the 268 said he was only able to see the rear of the 24X about eight railcar-lengths away.

The engineer applied dynamic brakes and independent brakes but “these braking efforts did little to reduce the train’s speed in the 17 seconds leading up to the collision,” the NTSB report said. The 268 was was moving at 13 mph at the time of the collision.