After train accident: inspectors warn of systematic problem with whisper brakes

They were long hoped for by residents living near busy railroad lines, but in Switzerland, they are now considered a risk: the use of so-called whisper brakes is believed to have caused the accident involving a freight train in the Gotthard Base Tunnel in August 2023. This is the conclusion of the final report by the Swiss Transportation Safety Investigation Board (STSB). What's more, the investigators do not see this as an isolated incident, but warn of a systematic problem.

The accident, which caused massive damage to the tunnel and a two-week closure, occurred when a wheel disk broke due to fatigue cracks caused by thermal overload. According to the investigation, all the wheels on the accident vehicle exhibited the same fatigue cracks – even the much younger ones. The STSB attributes this to the composite LL brake blocks used throughout Europe, which are marketed as “Low Friction — Low Noise” brakes. Due to noise protection regulations, they are replacing the cast iron brake blocks previously used.

DB has 60,000 freight wagons with whisper brakes

The issue is exacerbated by today's operating conditions: Freight trains no longer only travel at 60 km/h, but up to 100 km/h and have to brake correspondingly harder, which leads to higher heat generation. A European working group set up after the Gotthard accident discovered cracks in wagon wheels in 74 cases, and in 10 cases the wheels were already broken.

For Deutsche Bahn, the finger pointing at the brakes is probably inconvenient: It has now converted its entire freight wagon fleet of around 60,000 vehicles to the problematic LL brake blocks to meet the requirements of the Rail Noise Protection Act. In a statement published in the trade journal Lokreport, the company announced that “the rules of use and maintenance for wheel sets have been continuously adapted throughout Europe” in order to “reduce the mechanical and thermal loads on the wheels”. In addition to the regular wagon technical inspections and brake tests before each train journey, DB states that each wagon receives a supplementary inspection of the wheel shafts during workshop visits. The railroad refers to a European working group, which has dealt with damage to block-braked solid wheels with the participation of Switzerland.

SBB draw the consequences

Meanwhile, the Swiss Federal Railways (SBB) are drawing the consequences: SBB Cargo will “stop transporting wagons with LL brake blocks as soon as possible”, as Cargo boss Alexander Muhm announced. The transport ban is to be largely implemented by the end of the year and will remain in place until the EU Railway Agency and the Swiss Federal Office of Transport adopt “effective measures to modernize and improve the maintenance of freight wagons”. However, this should only partially allay concerns in Switzerland. Only around half of the freight trains crossing the Alps are operated by SBB. Railroad experts are therefore calling for border controls for freight trains in Switzerland, where overheated wheels could be detected by imaging measurements.

The STSB is making three key safety recommendations to the EU Railway Agency: an extension of the regulations on the minimum wheel diameter to all wheel set types with composite brake blocks, an adjustment of the maintenance specifications and a study on the influence of composite brake blocks on the thermal load on the wheels. The Swiss Federal Office of Transport believes that a solution is only possible at international level. Around 500,000 freight wagons with whisper brakes are in use across Europe.

(mki)