Leaves on the line & low rail adhesion
14 October 2011
"We apologise for the delay – this is due to slipping caused by leaves on the line.” It’s the announcement that causes eyes to roll, and heads to shake in disbelief.
But, come October, it’s a problem that this and every other railway has to face, and as the railway’s least favourite ‘season’ is underway, we thought it would be helpful for customers to explain how exactly ‘a few leaves’ can cause hundreds of tonnes of train to be delayed.
When leaves fall on to the line, particularly in damp or wet weather, the rolling action of passing wheels compresses them, causing a greasy ‘mulch’ to cover the rail.
This mulch is to rails what ice is to roads. It reduces the adhesion, or ‘co-efficient of friction’ to use the technical term, between wheel and rail. Acceleration must be reduced to prevent slipping, and braking distances extended. If you’re a regular customer, you can probably sense the wheel “slipping” on a train if you’re travelling through an area that’s affected. This is why minor delays are more prevalent at this time of year, particularly in the early morning and early evening.
The leaf mulch can also affect the operation of track circuits. Iarnród Éireann has machinery to address this problem, which operates overnight on key sections of the network, spreading “Sandite” on the line. However, this can only reduce the impact of leaf mulch rather than eliminate it. The mulch is Teflon-like, and even hand-scrubbing could not remove it. We’re not alone in this, as this article shows: http://en.wikipedia.org/wiki/Slippery_rail
The number of weeks this can continue for varies from year to year, depending on weather conditions. However, we will continue to work throughout the period affected to minimise delays on services, and apologise for the inconvenience caused.