A coach crashed in a tunnel in Switzerland last month killing 28 people. The vehicle impacted a wall head on, killing both drivers. No other vehicles were involved.

Peter Bishop, chairman of the Road Tunnel Operator Association said, “I’ve examined the photos carefully. The crash definitely occurred in a lay-by. It was not clear at first as it looked like a built-out structure. The tunnel is 2.5km-long with twin tubes very close together.

“The European Tunnel Register requires tunnels of this length to have lay-bys and safety niches. It seems that the driver lost control of the vehicle and mounted the kerb before hitting the wall.”

Swiss prosecutor Olivier Elsig said that there were a few possible causes of the crash. An autopsy would conclude if the driver was ill, though there was no evidence and that driver error was another possibility.

UK paper The Telegraph reported that the Swiss Federal Office for Roads was examining whether the angle of the wall increased the severity of the crash.

Bishop said, “The problem with permanently changing the angle of the wall, or introducing crash barriers is the deflection factor. The vehicle will deflect. This can be into the traffic of the tunnel and you can have a far worse accident involving many vehicles.

“It also comes to likelihood, the aperture of this lay-by measured against the entire length of the tunnel is very small. Crash cushions have been proposed in the past, but the angle of impact required is awkward in a tunnel.”

Belgian Transport Minister Melchior Wathelet said both drivers were well rested. They were hired to conduct tourists away from a ski resort and had arrived the night before, resting during the day before departure as per the law. No alcohol was found in the active driver’s blood and Elsig said there was no evidence of illness.

Elsig said the bus was new, and added that initial investigations suggested the coach was not exceeding the 100kph speed limit.

Swiss journalist Ruth Seeholzer told UK national media company BBC that driving conditions were normal and the two-lane tunnel was not busy with traffic when the accident happened.

A police spokesman said reports that the driver was changing a DVD at the time of the crash were “pure speculation”. Swiss newspaper ‘Le Matin Dimanche’ (‘Sunday Morning’) quoted the father of an injured victim saying the last thing his daughter remembered was a teacher approaching the driver with a DVD.

Investigations were ongoing as T&TI went to press. Bishop concluded, “Speed is the vital factor in tunnel crashes. It would have made an awful difference in this case as the smallest error of judgement is needed for a disaster. I don’t think a catastrophe of this magnitude could have been prevented, but we are pushing for speed reductions with the Highways Agency.

“All tunnel designers will now be looking at their structures. There is a forum in April near Farnborough, UK that did not have this accident on the agenda, but I think now it will be a serious topic.”