Study: Why do trains slip and wear in winter?

Published Feb 13, 2017

The tiny contact zone between the wheel and the rail, where steel meets steel, is roughly 1 cm2 in size and operates in the open, constantly exposed to a variety of natural environmental parameters (e.g. temperature, humidity and contaminants). This greatly influences the tribology (friction and wear), resulting in a loss of friction at the wheel-rail contact, which in turn results in delay and difficulty braking, which is a vital safety issue. In addition, wear at the wheel-rail contact causes a vast amount of components failure every year and costs billions of dollars.

In many high latitude regions, such as Nordic countries, Canada, USA, Russia etc, people face extreme weather conditions every winter. Understanding of the friction and wear problem at the wheel-rail contact is significant, but knowledge of wheel-rail tribology in conditions of subzero temperatures, with and without snow, is still a blank field.

Roslagsbanan, a railway close to KTH a winter morning.

In a research study at the KTH division of System and Component Design, Ph.D student Yezhe Lyu systematically investigated the tribology at the wheel-rail contact in temperatures ranging from -35 °C to 20 °C, with and without snow particle presence. Distinct unstable tribological performance was observed as a function of temperature and snow presence.

Extremely high wear was found around -15 °C as a result of the low temperature brittleness of the steel in both wheel and rail. At temperatures down to -35 °C, or with snow presence, a loss of friction was seen due to the generation of oxide flakes at the contacting path. Both situations are the last thing the railway operators and related organizations want to see.

Professor Ulf Olofsson is supervising Ph.D. student Yezhe Lyu to observe the morphology of natural snow particle.

The result was subsequently verified by one of the world’s largest train manufacturers, Bombardier, using railway service locomotives. After a complete analysis of the friction and wear mechanisms at various temperature levels (in terms of materials microstructure and property, snow physics and atmospheric physics), the findings were published in Nature Scientific Reports entitled “ Open System Tribology and Influence of Weather Conditions ”.

This study was performed in the Department of Machine Design, KTH Royal Institute of Technology, under the auspices of the KTH Railway Group, with the financial support of Stockholm Country Council, Traffic Administration and Swedish Transport Administration.

For further reading (the full paper):

Lyu, Y., Bergseth, E. & Olofsson, U. “ Open System Tribology and Influence of Weather Condition ”, Nature Scientific Reports.

Contact information:

Yezhe Lyu (

Dr Ellen Bergseth (

Professor Ulf Olofsson (