Thousands of tonnes of leaves fall onto railway lines every autumn, and we work hard to minimise the disruption they cause for passengers. We are expecting poor rail conditions across the South Western Railway network. This is likely to have an impact on our train services and may cause delays and alterations to train services.
Poor adhesion, often referred to as ‘leaves on the line’ is a problem which affects the railways during the autumn. Leaves falling onto the track are dragged under passing trains and crushed at a force of over 30 tonnes per square inch into a slippery paste. This is compounded during wet conditions where this wet slippery coating covers the rail and sets to form a hard Teflon like coating. The slippery rails make it difficult for train wheels to grip on the track.
Trains rely on friction between the wheels and rails in order to get grip, particularly while accelerating and braking. Because the top of the rails become slippery it can take trains longer to pull away from stations and they must also start to apply their brakes earlier. This means that trains can take longer to travel between stations and this in turn results in delays to the service.
We receive detailed weather reports from the Met Office which help us to plan for any weather related disruption to train services. Over the weekend a band of wind and light rain has been forecast to spread across our operating area- this presents the worst possible conditions in which slippery rails are likely to occur. We use this forecast together with data from our trains to predict the severity of rail conditions and have highlighted a very high risk of poor adhesion for this period.
Throughout the autumn period steps are taken to reduce the effects of slippery rails on our train service in conjunction with Network Rail. Special trains which spray the rail head with a high pressure jet of water to blast leaf mulch off of the track are run. Network Rail also delivered a major program of vegetation clearance to remove trees that have grown close to our tracks. These trees are replaced with varieties which are less likely to shed their leave onto the tracks and are planted further away from the railway.
During autumn leaf fall, leaves on the railway line cause problems. They create operational issues for the signalling system (track circuits) and reduce trains’ grip – this can change the ability of a train to start from a station, accelerate and climb hills, or stop at stations and signals.
Network Rail have 32 multipurpose vehicles and 29 locomotive-hauled rail head treatment trains (RHTT) – their dedicated, purpose-built equipment – that deliver autumn rail head treatment (RHT) programme. Both these types of train are equipped with a high-pressure pump delivering 1,500 Bar (2,200psi) and, if required, can apply adhesion modifier to each running rail.
Adhesion modifier is a mixture of suspension gel (so it can be pumped), sand (to help train wheels grip the rail), and steel or iron shot that is pushed through contamination (compressed leaves and debris) on the rail head to help the track circuits work correctly.