Investigation into North Zealand train collision could take months

The cause of Wednesday’s deadly train crash in North Zealand may not be determined for several months, according to a former senior accident investigator, as authorities begin examining technical and human factors behind the collision.

Danish public broadcaster DR reports that the crash—one of the most serious in recent Danish rail history—occurred when two trains collided head-on on a single-track stretch of the Gribskov Line between Hillerød and Kagerup. At least 17 people were injured, with five remaining in critical condition as of Wednesday evening. Seven others have since been discharged from hospital.

Bo Haaning, former head of the railway unit at Denmark’s Accident Investigation Board, told DR that piecing together the sequence of events would be a complex process. “It’s like assembling a puzzle—we need to find all the pieces,” he said, explaining that investigators must analyse technical evidence from the crash site, inspect the trains for faults, review data from the control centre, check for signal failures, and interview staff.

Haaning stressed that serious accidents rarely stem from a single error. “It’s usually a combination of multiple failures—technical, human, or procedural—that lead to such a catastrophe,” he said.

The stretch where the collision occurred operates with only one track for trains travelling in both directions, relying on station-based safety systems to prevent simultaneous use. However, Claus René Pedersson, safety chief at Lokaltog (the operator of the Gribskov Line), confirmed that this safeguard failed in Wednesday’s incident. “Our systems are designed to ensure only one train is on the track at a time. That did not happen here, and we must determine how this was possible,” he said.

The absence of an Automatic Train Control (ATC) system on the line—a technology that can automatically brake trains approaching red signals or exceeding speed limits—has drawn scrutiny. While Haaning noted that ATC could have prevented the crash, he cautioned that it was too early to confirm its relevance to this specific incident.

Kristian Madsen, a railway expert from the Danish Society of Engineers (IDA), told DR’s P1 Orientering that the collision appeared to result from human error, citing two likely scenarios: either a green signal was incorrectly issued to one of the trains, or a driver failed to observe a red signal. “This is an accident no one thought possible,” he said, urging authorities to prioritise installing ATC on the line despite cost considerations.

Train services on the affected route are expected to resume at 14:00 local time on Thursday. A total of 37 passengers were aboard the two trains at the time of the collision.