Slippery Slope: The 2009 Kaštela (Croatia) Train Derailment

Please note: It was a little difficult to find precise information on this accident. I still did my best, but some sections might lack their usual precision.


Kaštela is a city of 43349 people (as of 2017) in southern Croatia, located just 14km/9mi west-northwest of Split and 170km/105.5mi west of Sarajevo (both measurements in linear distance) right on the coast of the Adriatic Sea opposite to Italy.

The location of Kaštela in Europe.

Kaštela has several stations on the Knin-Split railway, a 103km/64mi mostly single track unelectrified main line. Opening in 1888 and rebuilt after 1991’s war for independence the line is used for everything from freight trains and regional passenger services to express trains and even international connections. The top speed on the line is 100kph/62kph, but the mountainous terrain on parts of the line demand much lower speeds in selected sections.

The approximate site of the accident seen from above.

The trains involved

ICN 521 was a passenger express service by the Croatian Railways (HZ) from Zagreb to Split carrying 90 passengers and two crew members (other sources claim 119 people on board). The service was provided by a Bombardier “RegioSwinger” two-car diesel multiple unit listed as series HŽ 7123. The RegioSwinger measures 51.75m/170ft in length at a weight of 116 metric tons and can reach up to 160kph/99mph. Each unit is driven by two Cummins inline-6 diesel engines producing 563 kW/755 hp each. The name RegioSwinger refers to the trains’ ability to lean into turns at up to 8° via electronically controlled suspension elements, allowing up to 30% higher speeds in turns compared to normal trains due to changes in how the forces of the turn affect the train and passengers. The trains also possess 3 independent braking systems, making them especially capable of operating on mountainous routes. The trains can carry up to 146 passengers in a two-class configuration. Since both halves of the train are technically identical they are individually numbered, usually with adjacent numbers (for example, unit 001 will be coupled to unit 002, 003 to 004 and so on), instead of giving the rear car a different designation.

A photo taken inside a German RegioSwinger with a level camera, showing the leaning body of the train.

The DB (German railway) originally ordered 192 units from Adtranz (which later became Bombardier Transportation) but only ended up taking 184. The remaining 8 units were sold to the HZ for 34 million Euros/39.9 million USD in 2005, despite local protests that the train was “overkill” for the intended use and not needed. The Croatian trains are largely identical with their German counterparts, save for a new paint job and some luggage space being traded for additional on board toilets.

HZ 7123 009/010, the unit involved in the accident, photographed in 2005.

Also involved in the accident was a Plasser & Theurer OBW-10 maintenance vehicle. These two-axle diesel powered vehicles contain a small crew cab, onboard crane and a flatbed section to load various tools, equipment or materials. They weight 25 metric tons empty and can reach a top speed of 80kph/50mph. Their crane is designed to lift cargo of up to 3.8 metric tons onto the vehicle.

An identical maintenance vehicle to the one involved in the accident, owned by the Israeli railways and photographed in 2014.

The accident

On the 24th of July 2009 at approximately 12:00pm ICN 521 is travelling eastbound through the mountains to the northwest of Kaštela. The extremely curvy route is exactly what the HZ bought the tilting train for, allowing higher speeds than what the locomotive pulled trains manage on the line. The train passed inspection just two days prior, attesting it spotless condition. As the train navigates a downhill section with increasingly tight turns it keeps picking up speed, exceeding the speed limit and continuing to accelerate. Eventually, at 12:07pm the train loses the fight against the centrifugal forces. The leading car derails in a sharp left hand turn through a cut in the rocks only about a kilometer/0.6mi from Kaštela-Sadine station, travelling at 133kph/83mph. The leading car falls against the rock wall, ripping open the driver’s cab and crushing most of the roof. Windows burst and the upper half of the wall folds in from the weight of the train pushing it against the rock wall, the rear car of the unit gets dragged along off the tracks and grinds along the wall. The completely derailed train actually leaves the cut in the mountainside relatively upright, digging into loose rocks and coming to a stop just a few meters from a steep ravine. Within seconds 6 people are dead, 55 get injured (some sources list 40 injured survivors).


Local residents from houses on the surrounding hillside are the first people to reach the wreckage, helping survivors off the train and notifying emergency services. The train derailed on a rugged hillside covered in loose rocks and soil, making it essentially inaccessible to cars, much less trucks. A few minutes after the accident the HZ sends a maintenance car to help in the rescue and recovery. Responders at the site end up having to jump out of the way when the maintenance vehicle runs out of control just like the RegioSwinger, derailing and barely missing the wreckage before coming to a halt further down the track. The crew on board gets relatively lucky and climbs out unharmed.

A video captured by a responder at the site, showing the maintenance vehicle speed past the wreckage as it derails much like the passenger train.

The derailment of the maintenance vehicle ahead of where the derailing passenger train destroyed the tracks rules out a mechanical fault on the train or sabotage (which had damaged a different RegioSwinger at an earlier point). While helicopters are brought in to take away the victims and survivors alike investigators start to examine the site and soon make an important discovery. The tracks at the site, as well as several hundred meters on either side of it are covered in a slippery, possibly oily substance. Calculations and later experiments show that this substance reduced friction for the trains so much that the RegioSwinger had no chance to slow down for the sharp turn, dooming it before it got anywhere near the site of the accident. The lower friction, which was caused by an essentially invisible coating on the tracks, meant the train would’ve needed three times as much distance to slow down for the turn.

The leading car of the involved train being recovered 2 weeks after the accident.

Once again it is the derailed maintenance vehicle that points investigators in the right direction. It had passed the site in the opposite direction just 10 minutes before the accident, spraying fire retardant. This was a regular occurrence as the area saw temperatures of as high as 40°C/104°F in summer, which meant sparks from the trains’ brakes could ignite the wooden sleepers or the adjacent bushes and grass covering the hillside, creating the risk of massive brushfires. As such the HZ regularly sprayed the wooden sleepers in a fireproof liquid meant to let them withstand the heat and sparks. Routinely one vehicle would spray the tracks with the retardant while a second one would spray the steel tracks with hot water to clean the retardant off them (as it obviously wasn’t needed on steel). However, the HZ had just recently changed the retardant they use, going with a liquid called TG-300 which was “a water-based resin” meant to soak into the wood and protect it long-term. Testing the material on a stretch of track it was noted that the hot water washed off most of the retardant, but left the exact yellow-brown film on the steel tracks that had been found where the trains derailed. Obviously either the retardant was generally unfit for railway use, or someone had neglected to adjust procedures to only spray the wooden sleepers but not the steel rails. Three days after the accident the warning “do not spray on tracks” was added to the manufacturer’s website.

The destroyed train in storage 2.5 years after the accident, with the leading car closer to the camera.

Three people at the head of HZ’s infrastructure division were fired following the accident, as were the two people in charge of purchase and application of fire protection chemicals. It took 11 days to clean the retardant off the tracks and allow traffic to resume once repairs were completed. The driver of the train, who survived with severe injuries, was expressively not the subject of a criminal investigation at any point.

The leading car from the RegioSwinger, still in storage in 2019.

Five people were eventually charged with premeditated gross negligence with fatal consequences, among them the director of HZ Infrastructure division, the HZ’s head of fire protection in the area and the fireman who oversaw the application of the retardant in the area. In May 2013 two of the defendants were sentenced to four and three years in prison respectively, including the overseeing firefighter. The remaining three defendants were acquitted. The sentence against the HZ’s head of ecology (four years in jail) was unsuccessfully protested and confirmed a year later.

The HZ has had continued bad luck with their RegioSwinger trains after the accident, minor accidents and defects knocked six of the remaining seven trains out of service and the seventh being written off after an accident with a truck. By 2013, only a single unit was left operational. However, by 2020 at least 4 units were in service judging from sightings by railfans.

HZ RegioSwinger 008/007, the once sole remaining operational unit, photographed near the site in 2013.

After the accident a small memorial was erected at the site of the accident, overlooking the bay and the city of Kaštela below. It consists of a small stone pedestal featuring a sculpture of a piece of rail forming the spine of a concrete leaf. The accident is the worst railway accident to befall Croatia since the fall of the Soviet Union and Eastern Bloc, which led to their separation from Yugoslavia, and as such remains unforgettable for locals.

The memorial for the accident, photographed a few years after the accident.


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Train crash reports and analysis, published weekly.

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