Wheel Slide Protection

The aim of this project was to reduce the risk of wheel damage on the Class 15X diesel multiple units due to leaf fall in autumn, by fitting a new Wheel Slide Protection System (WSP).

How does it work?

WSP is a system fitted to most passenger trains to prevent the wheels from locking up due to low adhesion between wheel and rail.

A sensor fitted to each wheelset provides pulses, representative of wheel speed, to the electronic unit on the vehicle. A comparison of the pulses from each wheelset is used to ensure that the wheelsets are working together.

If one of these signals deviates, or one or all of them decelerate at an unfeasible rate, the electronic unit detects a slide.

A signal is then sent to the relevant brake system on the affected bogie or axle, to release the brakes until the wheel returns to normal speed. At this point the brakes are reapplied.

In autumn 2016, one Class 156 unit fitted with our new WSP was operated in service at Greater Anglia . The results were remarkable with no wheel damage from flat spots seen and the unit remained in service for almost a year without requiring wheel reprofiling.

The first in class unit results were fed back to the wider industry and Porterbrook looked to roll out the modification to other vehicles. Greater Anglia and East Midlands Trains operated the same type of Class 156 units and by autumn 2017, a further 19 trains were fitted. The autumn 2017 results repeated the success of the first in class unit.

In 2018, Porterbrook continued to develop the design for other variants of the Class 15X units and produced a design for the single car Class 153 units. This time the design was implemented on a further 34 trains operated by Greater Anglia, East Midlands Trains and West Midlands Trains. Autumn 2018 performance showed that the system was also effective on these single car units.

In 2019, the Great Western Railway and Transport for Wales Class 150 fleets (53 trains) will be fitted in time for the leaf fall season. In addition, Porterbrook has shared the design more widely with other operators including ScotRail, which will fit its Class 156 fleet (43 trains) before autumn 2019.


Porterbrook Leasing, SNC-Lavalin, Loram UK, Knorr Bremse Rail Services and Greater Anglia received the “Engineering and Safety Award” at the Rail Industry Innovation Awards. The new Wheel Slide Protection (WSP) system has been successfully demonstrated in Greater Anglia’s Class 156 diesel multiple units.