Distracted Dispatching: The 2016 Bad Aibling Train Collision
By: Max S
Tags: Accident, Trains, Deutschland, Germany, Railways

The trains involved

While the stations and track itself are property of and operated by the DB (German national railway) the operation of the services on the line was taken over by the BOB (“Bayrische Oberlandbahn”) under their “Meridian”-brand in 2013. Using a distinct blue-gray-yellow livery for their multiple units the brand’s trains are easy to tell apart from the red DB-trains.

Travelling eastbound from Munich via Holzkirchen towards Rosenheim was DPN 7905, provided by a six-part third generation “Flirt” multiple unit coded ET 325. Made by Swiss train manufacturer “Stadler” the “Flirt” is a successful electric passenger multiple unit (with diesel- and hybrid versions offered also) mostly for regional passenger traffic, with over 1700 units being made since 2004 for railways in over a dozen countries including Germany, Switzerland, Great Britain and the USA. Introduced into service with Meridian in December 2013 the ET325 measures 107m/351ft in length and can carry 333 passengers (seated) in a two-class configuration, with space for up to 365 additional standing passengers. Weighting 179 metric tons empty the trains can reach 160kph/99mph, enough for their intended purpose. The trains are constructed to comply with the newest safety-norms, featuring special energy-absorbing elements below/in front of the driver’s cabin ensuring sufficient survival space at up to 36kph/22mph. The shape of the forward frame is also designed to keep one train from “mounting” the other’s frame in an accident, a common cause for severe damage to trains and passengers in collisions. Furthermore the cars are connected by special energy-absorbing joints, reducing the forces of cars hitting one-another in an accident.

ET325, the eastbound train, photographed in 2014.

Coming the other way on it’s journey from Rosenheim towards Holzkirchen was ET355, also provided by a Stadler Flirt 3. This train was smaller though, only being a three-part train. Weighting 114 metric tons the capacity is reduced to 158 seats in two classes and space for 226 standing passengers. The top speed remains the same, with the lower weight allowing a slightly faster acceleration especially at low speeds. The trains are identical on the technical side, with the ET355 essentially just missing 3 center cars but having the same safety-equipment. ET325 has a data-logger in each control cabin with the forward-one recording data as the train moves, while ET355 has one data-logger recording data regardless of the train’s direction of travel.

ET355, the westbound train, photographed in 2014.

The Accident

On the 9th of February 2016 39 years old Michael P. is working in the signal box at Bad Aibling station, preparing the paths and stops for the day’s trains. He’s been working as a dispatcher for the DB since 1997, Bad Aibling was the first signal box he was trained at. He had also passed mandatory training for unusual situations, including signal failure, in 2010, 2012 and 2014. At 6:38am he sets a section of the path for DPN 79506, the westbound connection provided by ET355. His input sets the points and signals both for the arrival at Kolbermoor station and the departure towards Bad Aibling. The train arrives at 6:40am and is scheduled to stay at Kolbermoor station until 6:45am to wait for the oncoming DPN 79505 (provided by ET325) to pass and clear the single-track section to Bad Aibling.

A simple visualization of the route and either train’s direction. The red dot is the accident site.

On the day the ET325 has a 4 minute delay, usually this would mean the westbound train waits a little longer. It’s Shrove Tuesday, no school and few people working. The trains are almost empty, there’s no rush. Only approximately 150 people are on board (the operator later admits they always have to assume a few people ride without buying a ticket), including the two drivers and a driver in training who is riding in the driver’s cab of ET355 to learn the route before driving it on his own.

Since the dispatcher already set the path for ET355 all the way to Bad Aibling ET325 now can’t depart from Bad Aibling station, the single track section is reserved and the signals cannot be turned green. ET355 will be proceeding as scheduled, the system moved the meeting point of the two trains to Bad Aibling station.

Signals at Bad Aibling station (eastern exit). Note the small square replacement signals.

The dispatcher suspects a signal failure, an error in the “counter motion protection” (“Gegenfahrschutz”), the system meant to keep opposing trains out of a single track section. Protocol would now require him to check the neighboring block zones to ensure there are no opposing trains. He neglects to do this, immediately jumping to the course of action for cases when there definitely is just a fault in the system. He activates the replacement signal at Bad Aibling station, overriding the order to stop and disabling the auto-stop of running a red signal. ET325 departs the station and proceeds 870m/2855ft to the block-signal at “Bad Aibling Kurpark”, at Kilometer 28.73.

A comparison from the report, between “stop” and “stop” being overridden.

The block-signal at Bad Aibling Kurpark, the last chance to stop the train.

Still suspecting a fault as this signal won’t turn green either the dispatcher clears the train to proceed with the replacement signal here also, again neglecting proper procedures. The lights on the replacement signal turn on at 6:45am, ET325 proceeds past the signal just as ET355 leaves Kolbermoor. The trains are now on collision course, no more signals along the way can stop them. Now the dispatcher realizes what he’s done, and hurries to send out an emergency stop order. The route along the Mangfallkanal goes around a left hand (for the eastbound ET325) bend, due to the dense woods on the inside of the turn the train driver’s can’t see very far ahead. Adding to that problem is the time of year, while the weather is clear it is still dark. In his hurried panic the dispatcher hits the wrong button, his message goes out to surrounding dispatchers instead of trains at 6:46:20am. At the same time the driver’s suddenly face each other as their trains come around the corner. ET355 is travelling westbound at 52kph/32mph, ET325 is coming the other way at 87kph/54mph. Both trains register the driver triggering an emergency stop at 6:46:55. One second later both trains collide head-on at Kilometer 30.29, without having lost any speed. All 3 drivers are killed on impact, the energy-absorbing elements on either train’s nose are utterly outclassed by the violent impact. The anti-climb elements work in some capacity, instead of mounting one-another and crushing the lower train’s interior ET325 is deflected as it starts to climb, tearing the wall off ET355’s forward car almost entirely as it starts to lean to the right, nearly falling over. A total of 11 people die in the collision, 90 are injured (28 of which severely).