The dreaded wisselstoring

Martin Hiensch, a railway engineer with 25 year of experience, explained what’s behind switch failure and outlined solutions he’s working on in his research.

Sponsored by the Materials Innovation Institute (M2I) and Prorail, Hiensch is studying the sustainability and increasing the performance of rail switches in his PhD research at the Railway Engineering Section of the Civil Engineering faculty. He said switches are the most vulnerable part of track infrastructure and when they fail it has a huge effect on operations. They have curved rails and movable parts exposed to varying weather conditions and are subjected to large dynamic stresses when shifting trains between tracks. A study by several rail companies in Europe identifies the extreme wear of switches as one of the top three reported track problems.

“Straight rails can last for up to 40 years,” said Hiensch. “In contrast curved rails have a 15 year lifespan, and in some parts of the Dutch rail network, switch rails have to be replaced every three months.”

With the Dutch rail network currently transporting 1.2 million passengers a day on 6,550 trains, the demands made on the system’s 7,000 switches have increased. The loading of the tracks is much greater due to passenger numbers and freight tonnage growing every year. Also modern trains are designed for passenger comfort at higher speeds, but this has worsened their curving behaviour. Their more stable, stiffer bogies subject curved rails and switches to more wear. Intensifying track maintenance only tackles the symptoms.

“Track deterioration is strongly influenced by train characteristics,” he said. “Track development has lagged behind train development and it took a long time to understand the change in damage behaviour on the track.”

Hiensch says to properly accommodate increasing rail transport capacity you can make the switches more robust or reduce the loading imposed by the trains. But he is looking at both, considering the wheel-rail interface as a system. To understand the expected wear he uses validated vehicle and track simulation tools. Using damage models he evaluates the type of wear and fatigue and then considers optimisation possibilities of both train and switch design.

His results show that existing train bogies can be made more track friendly by fitting improved dampers. These are frequency dependent and modify wheel behaviour depending on whether the train is going straight or curving. They lower the forces on switches by up to 40% and impact significantly on their lifespan. This type of damper is already applied in road vehicles and has been tested on real tracks in the Netherlands in 2016 with positive results as an important first step towards full implementation. Apart from reducing contact forces, possible added benefits are reduced energy losses and less noise in curves.