Slippery rail
The condition results in significant reduction in friction between train wheels and rails, and in extreme cases can render the track temporarily unusable.
[4] In heavily deciduous forested areas like the American Mid-Atlantic states, New England, many parts of Europe including the UK, and Southern Ontario, Canada, the problem can arise.
Where the leaves fall onto a railway route, some collect on the railhead and are then heavily compressed by trains into a slippery low-friction coating on the rail and on the wheel treads.
A light rain shower following a long period of dry weather can sometimes cause similar low adhesion conditions to those of leaf fall contamination.
Since then, disc brakes have increasingly been used, which means that cleaning the compressed leaf material from the wheel tread by abrasion no longer occurs.
[12] A report by England's Commissioners of Railways of May 1851 noted that an accident was caused when a small locomotive hauling a heavy train was unable to find purchase on the rail because by the dirty state of the track ballast.
As the railways ceased to use steam traction, this maintenance was allowed to lapse, and the resulting extra growth increases the supply of leaves thereby exacerbating the problem.
In Victoria, Australia, train wheels crushing plagues of introduced Portuguese millipedes which were crossing the tracks, caused passenger rail operator V/Line to be penalised more than $700,000 for cancellations and poor punctuality in one quarter of 2001.
[15] In 2009, railway tracks at Tallarook in central Victoria were also affected by a Portuguese millipede plague, causing several trains to be cancelled.
In extreme cases, the build-up of leaf material can electrically insulate the wheels from the rails, resulting in a failure of signalling equipment to detect the presence of the train.
[22] Lineside-fitted Traction gel applicators[23] which apply liquid to the railhead as a train passes are fitted at sites where significant low adhesion regularly occurs, such as on the approach to stations.
One method uses solid CO2 ("dry ice")[25] which is fired at the track through a nozzle, removing commination through surface cooling, kinetic energy and sublimation.
Using lineside markers each driver gets their train up to speed and then makes a full service brake application under normal adhesion conditions.
Although this provides only an approximation of how a train will behave during low adhesion, it does ensure that the driver can recognize the onset of wheel slide and will know the correct actions to take when it occurs.
In the UK, some passenger train operating companies publish a special 'leaf fall' timetable[29] to allow for the additional time that lighter braking and acceleration take.
In the UK there are several sources; Removal of deciduous trees at the lineside is a management method to control the problem; however, there is political resistance to this in populous areas.
These trains consist of a pressure washer and gel dispenser mounted on a converted flatcar, and a tank car which carries water.
These trains are timetabled to run between scheduled daytime services as well as during the night when less rail activity can allow the railhead contamination to build up.
[42][43] Particularly problematic local trees include the sycamore, lime, sweet and horse chestnut, ash, and poplar, which regrow or coppice after cutting back, and have large, flat leaves, which stick to the line and cause severe slippery rail.
