Leaves on the Line
Autumn comes around at the same time every year - and for the millions of passengers on Britain's railway network, the shadow of delays blamed on leaves on the line looms large.
The "wrong type of leaves on the line" have become a standing joke in recent years.
Most native trees in Britain are deciduous - they shed their broad flat leaves each autumn as the days shorten, temperatures fall and winter approaches.
Leaves on the line cause major delays and costs the rail industry tens of millions of pounds a year - and resulting in untold misery for users.
What is the problem?
- Network Rail is the private company in charge of maintaining 20,000 miles (32,000 km) of track and the land bordering it in Britain - much of it is tree-lined
- Network Rail estimates that tree leaves falling on the rails each autumn cause half-a-million "delay minutes"
- Network Rail spends tens of millions of pounds a year on leaf removal
- a mature broadleaved deciduous tree can produce - and shed - up to 50,000 leaves each and every year
- fallen leaves are swept onto the rails by the wind and the slipstream of passing trains
- leaves made damp by rainfall or autumnal dew adhere to the rails
- trains running over them then crush and bake the wet leaves at high pressure making a hard, smooth Teflon-like coating on the rails
- this film of baked leaf acts like "black ice" on the rails so trains slip, losing traction and reducing braking ability - which results in delays and is potentially dangerous
- the hard slippery coating on the rails is hard to remove
- particularly problematic trees are those like sycamore, lime, sweet and horse chestnut and those which re-grow or coppice after cutting back - or both - with large flat leaves which tend to stick on the lines
- known trouble spots include deep cuttings and steep inclines
Are there solutions?
- in the days of steam trains, leaves on the line were seldom a problem as trees and scrub were regularly cut back by railway gangs to prevent stray sparks starting fires
- but as steam trains phased out, line-side maintenance lapsed and the trees began to grow back and encroach on the lines - trees were sometimes planted to improve landscape and muffle train noise too
- the trains replacing the steam trains - explain the experts - had block brakes which helped to stop leaf debris encrusting both wheels and rails
- but the modern fleet of lighter weight diesel and electric trains have disc brakes, more liable to a build up of debris from the rails
- Network Rail have a cocktail of weapons to combat autumnal leaves including:
- o cutting down trees
- o using hand-held petrol-driven scrubbers to clean the rails
- a fleet of engineering trains travelling the rail network, removing leaves ahead of them with high-pressure water jets and with spreaders at the rear smearing a mixture of sand and gel - "Sandite" - on the rails to aid grip
- o the Sandite applicator is the road equivalent of a gritting lorry
- some "state-of-the-art trains boast "smart sanders" which detect wheel slip and automatically release sand to help traction
- at least one train company has even resorted to adjusting its timetable in the autumn - warning passengers to add a few minutes development work on a high-power laser system to clean railway tracks of grease, ice, rust, rubber and other contaminants as well as encrusted leaves looks promising.
- over-zealous or inappropriate clearance of trackside scrubs and trees generates backlashes too and can destabilise
- embankments and facilitate landslips
More about how and why tree leaves drop in the autumn and the species of trees mentioned here - are on our RFS Website.