Home Correction journal Targeted noise correction leads to quieter freight trains

Targeted noise correction leads to quieter freight trains


Imagine a sinister bogeyman perched on the bed of an exposed railroad freight car. As the train rolls through the night, he slams a hammer on a heavy anvil and a metal rasp sounds. Throughout its journey, the noise is greater than the noise generated by the entire train, waking the dazed workers in their rooms and exhausting the line’s noise quota.

Several types of wear or defect in a railcar will cause the kind of pounding noise our freight gremlin emits, but few realize the implications of just one of these defects for the many stakeholders in the rail industry. Indeed, few realize that a dominant noise determines the noise level of the train as a whole.

As political ambitions crystallize in national regulations, noise emissions are impacting rail freight operators’ efforts to increase traffic. Excessive noise reduces routing options for new lines.

A bad axle has an impact on the sleep of people along the road, but it also has an impact on hospitals for which the interruption of patient sleep translates into a higher incidence of high blood pressure, accident stroke and heart disease. Ultimately, a noisy axle is a dead weight on any effort to increase rail freight.

Providing a way to get the noisy bogeyman – the damaged wheel or faulty axle – out of the train is the aim of Nemo, a recently launched project funded by the European Union (EU) Horizon 2020. It is hoped that by allowing maintenance to be planned at the exact source of a noise problem, an obstacle to the expansion of rail freight can be removed.

“What people don’t realize is that the biggest noise contributor dominates everything else,” says Mr. Nathan Isert, noise research specialist at Müller-BBM Rail Technologies, a member of the Nemo project based near Munich.

“Suppose a wheel has developed a puncture on its running surface following emergency braking. With each turn, the axle will drop suddenly as the flat hits the rail head, then bounce back, effectively pounding the rail and bogie above. This one flaw has now altered the sound emissions of the Expedition as a whole.

Historically, railways were built without regard to noise. More recently, new lines have been subject to noise quotas, but only during construction. Train capacity has been calculated on the basis of standard, well-maintained vehicles compliant with the Technical Specification for Interoperability (TSI). The planning process naturally focused on land and infrastructure as it was. This meant fewer trains than today and fewer residents living near the tracks. Trains ran less frequently at night.

Quieter policies

But things have changed. The demand from the passenger network means that freight must be transported largely at night. In this context, the EU and many national regulators are increasingly looking to protect residents from the resulting noise burden.

The freight industry has been committed to these political ambitions since the early 2000s. More recently, noisy braking systems have been banned in Switzerland and Germany.

Switzerland’s Noisy Freight Wagon Act and Germany’s Noisy Freight Train Ban Act led Germany’s largest rail freight operator, DB Cargo, to replace the noisy iron brake blocks of 63,000 wagons with composite brake blocks. Apparently, this led to a modernization of all freight wagons in Germany and Switzerland and thus to a halving of the perceived noise of a freight shipment. Although freight trains are frequently measured at 80dB or more, the logarithmic scale used to measure noise means that a bystander experiences the 10dB reduction that can be achieved by replacing cast iron with composite brake shoes like nearly half the noise reduction.

In January 2021, the German government and German Rail (DB) went further by announcing an initiative to add 125 km per year of noise reduction measures on tracks and rolling stock. It is planned to add 1,250 km to the existing 2,000 km of noise routes by 2030.

The technology we are assembling will include microphones to measure noise, cameras to capture UIC identification number and brake type, and other instruments that will locate a noisy fault on a specific train car.

Nathan Isert

Since freight wagons are transcontinental, a single national regulatory act often impacts the rail industry in continental Europe.

Isert says the ultimate stakeholder is the national regulator, but unsurprisingly things get more complicated the further down you go to the individual wagon where a fault may occur.

Infrastructure managers face a large part of the regulatory burden, while rail operators face higher costs when the infrastructure manager reduces the number of vehicles to reach average noise limits. Owners of freight wagons had to face considerable costs for the modernization of the brakes, reaching 200 million euros in the case of DB Cargo.

But it doesn’t stop there as penalties are introduced. A non-compliant shipment can face a €50,000 fine in Switzerland, while in Germany operators would face a €1,500 fine if a wagon with the oldest iron brake shoes is discovered. Germany has made public its intention to introduce a train path pricing system that adjusts charges according to the level of noise emissions or the installation of mitigation technologies.

With so much at stake, the Nemo team is currently working to bring together a range of technical solutions into a single monitoring system.

Policy makers are increasingly seeking to protect residents from excessive noise emitted by freight trains traveling through urban areas. Photo: Shutterstock/Hans Engbers

“The technology we are assembling will include microphones to measure noise, cameras to capture the International Union of Railways (UIC) identification number and brake type, and other instruments that will locate a noisy fault on a specific car in a train,” says Isert.

A software system must analyze the noise measurements and isolate each car by virtually filtering the noise of the neighboring car. The UIC number is recognized in characters and sent to a database for verification, after which key metrics are associated with a noise record.

Separate instruments have now identified the affected axles and software then classifies the difference between the loud noise of a wagon and the noise limit. This comes from the European Commission, which has published TSI levels for particular types of wagons. In this last step of the software, the noise measurements are normalized for the train’s reference speed of 80 km/h.

“It’s a lot of data, but we keep it simple by using a traffic light system,” says Isert.

“When an individual car is more than 3 dB above the limit, it will get a red light. This way, a single intervention to reduce the noise of this fault can benefit the whole system.”

The Nemo team is working with industrial partners on a demonstration of the technology which will take place in the south of the Netherlands in the spring of 2022.

The demonstration is part of a broader remit of pioneering European technological innovations that can identify outliers with particularly excessive emissions. Research for Nemo in Madrid, for example, has already shown that just a few vehicles are responsible for the lion’s share of air pollution.

Peripheral road vehicles, trains and ships will be identified along with noise pollution mitigation measures. The overall objective of the project is to drastically reduce emissions in cities by 20% for noise and 30% for air pollution.

Isert believes there are tremendous benefits for everyone involved in identifying outlier issues. “It really depends on industry acceptability,” he says. “Huge investments can be wasted if we don’t find a way to identify these noise defects and communicate them to owners and operators so that corrective action can be taken quickly.

“Hopefully we will reduce noise that is essentially unnecessary, while reducing costs for businesses involved and disruption for people nearby.”