Background
Mühlheim (Main) is a city of 28752 people (as of December 2019) in western Germany, located 16km/10mi east of Frankfurt and 4km/2.5mi west of Hanau (both distances measured in linear distance).
The city lies on the southern bank of the river Main (hence the name) and is crossed west to east by the Frankfurt Hanau Railway (also called the South Main Railway), a 23km/14mi long double-track electrified mainline. Opened in it’s current expansion in 1875 the railway is engineered for a top speed of 160kph/99mph and sees everything from regional trains to long distance express trains and freight service, being one of the busiest express routes in Germany. Located on limit space the local S-Bahn (an urban rapid transport service) runs alongside the two tracks for most of it’s length, mostly between the railway and the river. Just east of Mühlheim an underpass brings the S-Bahn from the south of the railway (where it’s located within Mühlheim) to the north of the tracks.
The vehicles involved
Travelling westbound from Frankfurt towards Wächtersbach is RE (Regional Express) 15640, consisting of 6 bilevel passenger cars and a DB (German national railway) Series 111 electric locomotive. At the time of the accident the train is going in reverse, with the locomotive being remotely controlled from a driver’s cab in the control car at the other end of the train. The train cars are all third Generation Bombardier bilevel passenger cars, with the control car carrying the model-code DBbzfa. Introduced into service between 1995 and 1997 the control car weights 48 metric tons at 27.27m/89ft long and can carry 101 passengers in it’s purely second class interior. The other 4 second class cars in the train weight 46 metric tons each, and can carry each 139 passengers, with the mixed first/second class car ahead of the locomotive offering 108 seats. However, the night of the accident the train is nearly empty, only carrying the driver, a conductor and 34 passengers. All the cars have a top speed of 140kph/87mph, enough for the regional traffic.
The DB had planned to replace some pieces of the S-Bahn’s track near the eastern edge of Mühlheim during the night, using the lower traffic at night to cause less chaos with the schedule. Since the construction site was inaccessible to trucks and other road vehicles a company with a so-called dual mode excavator was contracted to help. Dual mode vehicles (also called road-rail-vehicles) are specialized vehicles (usually construction equipment) who can lower a set of train wheels outside their rubber tires, allowing them to travel on train tracks. In this case, the excavator was meant to drive to the construction site on the tracks and then serve as a crane to lift the track pieces out of and into place. The excavator used is a Liebherr 900 Litronic, weighting about about 20 metric tons. It was driven by a construction worker who was also qualified as a train driver, carrying another construction worker on the vehicle with him.
The accident
On the thirteenth of April 2012 the driver of the excavator radios the railway-dispatcher at 0:27am, asking permission to set the excavator up at a level crossing approximately 2km/1.2mi west of the construction site. Originally he asks for the S-Bahn track to be shut down for this, but then reconsiders (presumably the excavator wouldn’t have fit through the tunnel) and asks to have the track from Hanau main station towards Mühlheim (the northern track) blocked. He receives permission to use the track at 0:31am and reports to be in position at 0:38am. For unknown reasons he passed the blocked northern track and set his vehicle up on the southern track, which is still open for traffic. To make matters worse the excavator only reports it’s position to the signal box at individual points, not constantly. It’s unknown if the driver knew he was on the wrong track, the dispatcher certainly had no way to know it. The driver of the excavator starts driving eastbound, while his coworker is standing on the outside of the vehicle, holding on to the cabin.
At 0:56am RB 15460 departs nearby Offenbach station and begins to accelerate. It’s a clear night without rain or even clouds, giving relatively good visibility. The data-logger aboard the control car registers a steady acceleration as the nearly empty train picks up speed. At this point, the collision is all but unavoidable. The train reaches 129kph/80mph before it slams into the nearly stationary excavator at 0:58am, compressing the driver’s cabin and killing the train driver on impact. The force of the impact is so severe that it buckles the massive train car behind the driver’s cab, pinching the forward doors shut. Both wheel sets of the control car derail causing the control car to swerve left and right slightly, with the data-logger registering it changing the side of the track it’s on several times over the next 12 seconds. The derailed train car pushes the derailed excavator along for another 405m/1330ft after the collision, ramming three overhead wire supports. The driver of the excavator doesn’t survive the collision with the train, his coworker is thrown off and dies also. The conductor later recalls just entering the control car to check the tickets, and suddenly being thrown down the length of the car against the glas wall separating the passengers from the driver. As he regains consciousness he notes the floor of the car being at a strong incline. With the forward doors inoperable he releases the rear doors and guides passengers out of the stopped train. He and 13 passengers require medical attention, 6 of which for severe injuries, 21 survive the collision uninjured.
Aftermath
The conductor and at least one other passenger call the emergency services, the alarm is issued at 1:06am. Within the next hour 150 responders arrive on scene. With the DB confirming that the overhead wires are switched off they start by securing the train car with heavy duty cables and ratchet straps, the accident had left the control car leaning to the right and responders feared that it might fall over when they work on it. With all survivors taken care of the firemen start cutting the excavator and control cab apart, by 11am the body of the train driver can be recovered. The excavator driver’s body is also found between the two vehicles, it’s unknown if the vehicle was stopped and he’d for some reason walked around it or if the force of the impact threw him out the back of the cabin, into the front of the train. Originally it’s suspected that the construction crew hadn’t waited for the track to be closed, or maybe a train had been sent onto the blocked track by mistake. But records from the signal box soon show that this was not the case, when a track is blocked a train cannot enter it by accident. The system wouldn’t allow a path to be set into a blocked track and the signals wouldn’t turn green, keeping the train from departing.
Two days after the accident the excavator is taken away on a flatbed and most of the train, having been barely damaged, leaves the site also. The DB brings in two special heavy duty cranes to lift the wreckage of the control car off the track, having been damaged too severely to be towed away. After that workers replace 500m/1640ft of track, ballast and overhead wires before the railway line can be reopened. The total material damage comes in at 1.89 million Euros/2.3 million USD, excluding medical and therapy cost.
The official report is released on the 15th of July 2014, revealing a morbidly random cause. There is no other way to explain the accident than that the driver of the excavator stood at the level crossing, knew one of the two tracks in front of him was blocked for his vehicle, and didn’t know which one. And instead of asking the dispatcher he chose randomly, like flipping a coin. And he got it wrong.
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