Why leaves on the line cause such an issue
Electrical Engineer Stuart Brown explains why and how can ESG help
Here, our Principal Electrical Engineer Stuart Brown, an expert in low adhesion braking performance, explains why leaves on the line cause such an issue and how ESG Rail, as the experts in rolling stock, can help operators and rolling stock owners in minimising the costs and disruption often associated with leaves on the line.
WHY IS THE RAILWAY MORE SENSITIVE TO LEAVES THAN OTHER TRANSPORT MODES?
Both road and rail networks have cuttings, which trap leaves exacerbating the adhesion problems caused, however the issue is worse for the rail network. Obviously, road and rail vehicles and their equivalent surfaces are made of different materials, explaining some of the difference. However, the main problem actually arises from the different contact patches between the wheel and surface. In a rail vehicle the contact patch is typically about the size of a 5 pence coin, for a road vehicle it is significantly greater. This gives a rail vehicle a low rolling resistance, which makes it an efficient form of transport. Conversely, it also places a greater dependency on the contact patch to do the braking or accelerating.
SO WHAT IS HAPPENING TO CAUSE THIS SLIPPERY RAIL?
Basically, the leaves fall from the trees onto the rail and are then crushed onto the track by the trains running over them. Crushing the leaves releases a substance called Pectin that is held within the leaf cell walls (the same material used in the food industry as a gelling agent to make jam and jellies). The Pectin in the crushed leaf in combination with water forms a very slippery film. Leaves that are compressed onto the rail are also known to be very resistant to removal. Research work undertaken by the Railway Safety Standards Board and Imperial College has investigated this issue and can be found at http://www.rssb.co.uk/library/research-development-and-innovation/research-brief-T354.pdf and (http://link.springer.com/article/10.1007%2Fs11249-006-9152-2).
When the train driver applies the brakes on a slippery rail it causes the wheels to decelerate faster than they should. This can lead to damage occurring on the wheels known as “wheel flats” and also affects the ability of the train to stop. This is potentially dangerous in extreme conditions. Thankfully, these extreme conditions do not occur too frequently.
Since the mid 1970’s UK passenger trains have been fitted with electronic equipment called WSP-Wheel Slide Protection, which is very similar to ABS on cars and helps to protect the train wheels as much as possible when slippery rail conditions occur. The WSP controller operates under a set of rules or algorithm. Modern WSP systems use software to do this. From the perspective of safety and maintenance, it is important for the rail industry to be able to get the best performance that it can from the software on the train, to minimise the stopping distance of the train and to avoid damaging the wheels.
HOW CAN ESG RAIL HELP?
ESG has brake system technology called WSPER (wheel slide protection evaluation rig). This ‘hardware in the loop’ simulation tool improves operational safety, reduces whole life maintenance costs and maximises braking capability in all adhesion conditions. It does this by testing the WSP controller and its software algorithm against a wide range of slippery track conditions. Effectively, the WSPER fools the WSP equipment into thinking that it is fitted on the train.
WSPER is unique, it holds data obtained by British Rail Research that was recorded by a test train travelling around the rail network measuring dry and slippery track conditions.
HOW CAN WSPER HELP A TRAIN'S PERFORMANCE IN LOW ADHESION?
WSPER provides a way of objectively and consistently assessing the performance of the WSP algorithm for a particular train braking system application.
WSPER can also help by measuring the effectiveness of adhesion equipment, such as sanders.
TALK TO THE EXPERTS
To talk to an expert about any issues you may be experiencing with braking performance, contact us directly via firstname.lastname@example.org