PICTURE a sinister bogeyman perched on the flat bed of a rail freight wagon exposed to the open sky. As the train rolls through the night he slams a hammer onto a heavy anvil and a metallic rasp rings out. Along its entire route, the noise is greater than the sound generated by the entire train, waking dazed workers in their bedrooms and using up the line’s noise quota.

Several kinds of wear or fault in a wagon will lead to the kind of hammering noise our freight gremlin is emitting, but few realise the implications of a single such fault for the rail industry’s many stakeholders. That is because few realise that a dominant noise sets the noise level of the train as a whole.

With policy ambitions crystallising into national regulations, noise emissions are impacting rail freight operators’ efforts to increase traffic. Excessive noise reduces the routing options for new lines.

One bad axle impacts the sleep of those along the route, but it also impacts hospitals for whom interrupted sleep for patients translates into higher incidence of high blood pressure, stroke and heart disease. Ultimately, a noisy axle is a dead weight on all the efforts to increase rail freight.

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

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

“Say a wheel has developed a flat on its running surface from emergency braking. With each revolution, the axle will suddenly drop as the flat touches the rail head and then bounces back, effectively hammering the rail and bogie above. That one fault has now changed the sound emissions of the shipment as a whole.”

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

Quieter policies

But things have changed. Demand from the passenger network means that freight must be largely transported at night. Against this backdrop, the EU and many national regulators are increasingly seeking to protect residents from the resulting noise burden.

The freight industry has been engaging with these policy ambitions since the early 2000s. More recently, there have been bans of noisy braking systems in Switzerland and Germany.

The Swiss Loud Freight Wagon law and the German Loud Freight Trains Prohibition Act caused the largest German rail freight operator, DB Cargo, to replace noisy iron brake blocks on 63,000 wagons with composite brake blocks. Ostensibly this has led to a retrofitting of all freight wagons in Germany and Switzerland and thereby 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 for measuring noise means a bystander experiences the 10dB reduction that can be achieved by swapping iron cast for composite brake blocks as a near halving of the noise.

In January 2021, the German government and German Rail (DB) went further, announcing an initiative to add 125km a year of track and rolling stock noise abatement measures. It is planned to add 1250km to an existing 2000km of noise-abated routes by 2030.

The technology we are assembling will include microphones to measure the noise, cameras to capture the UIC identification number and brake type, as well as further instruments that will localise a noisy fault to an exact wagon on a train.

Nathan Isert

Since freight wagons are trans-continental, a single national act of regulation frequently impacts the continental European railway industry.

Isert says the ultimate stakeholder is the national regulator, but predictably things get more complicated as one traces down to the individual wagon where a fault may arise.

Infrastructure managers face a large part of the regulatory burden while train operators face higher costs when the infrastructure manager reduces vehicle numbers to hit average noise limits. Freight wagon owners have faced considerable costs for brake upgrades, reaching €200m in the case of DB Cargo.

But it doesn’t stop there as penalties are being introduced. A non-compliant shipment can incur a €50,000 fine in Switzerland, while in Germany operators reportedly face a €1500 fine if a wagon with the older iron brake blocks is discovered. Germany has made public its plans to introduce a train path pricing system which adjusts charges depending on the level of noise emissions or the installation of mitigating technology.

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

Policy makers are increasingly looking to protect residents against excessive noise emitted by freight trains travelling through urban areas. Photo: Shutterstock/Hans Engbers

“The technology we are assembling will include microphones to measure the noise, cameras to capture the International Union of Railways (UIC) identification number and brake type, as well as further instruments that will localise a noisy fault to an exact wagon on a train,” Isert says.

A software system must analyse the noise measurements and isolate each wagon by virtually filtering out the neighbouring wagon’s noise. The UIC number is character-recognised and sent to a database for verification whereupon key metrics are associated with a noise record.

Separate instruments have by now identified the axles involved 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 wagon. In this final software step, the noise measurements are normalised for the benchmark train speed of 80km/h.

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

“Where an individual wagon is more than 3dB louder than the limit, it will get a red light. This way a single intervention to reduce noise from that fault can realise benefits for the entire system.”

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

The demonstration is part of a wider remit to pioneer European technology innovations which can identify outliers whose emissions are particularly excessive. Research for Nemo conducted in Madrid, for example, has already demonstrated that just a few vehicles are responsible for the lion’s share of air pollution.

Outlying road vehicles, trains and ships will be identified along with noise pollution mitigation measures. The overall project goal is to radically reduce emissions in cities by 20% for noise and 30% for air pollution.

Isert believes there are considerable benefits for everyone involved in identifying outlier problems. “It really comes down to the acceptability of the industry,” he says. “Huge investments can go to waste if we don’t find a way to identify these noise faults and communicate them to owners and operators so corrective action can be taken quickly.

“Hopefully, we will reduce noise that is essentially unnecessary, while reducing costs for the companies involved and disturbance for those nearby.”