Sandite is a solution made up from antifreeze, sand and steel-shot (tiny round steel grains). It is used on the UK rail network to combat that age-old-problem of "leaves on the line".
Leaves on railway tracks can cause massive disruption even though trains weigh several hundred tons or more. This is because train wheels can easily slip on the mulch that compressed wet leaves turn into if left unattended.
Another problem is when leaves insulate track from the metal wheels of the train. This connection is vital as the train wheels and axles are what creates an electrical circuit between the two parallel rails and therefore lets the signal box or operations room know where the train is. Without it the train simply disappears from the control panel.
Special trains equipped with Sandite application facilities operate during the autumn period across the network. Train staff are made aware of track stretches vulnerable to mulch build-up by a series of black on yellow warning signs advising operators when the stretch is approaching, when to commence and when to end the application of Sandite.