 During autumn, a fleet of Railhead Treatment Trains (RHTT) run across the network using high pressure water-jetting to clean the railhead.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.The cryptic nature of rail company explanations for slippery rail and related phenomena made the phrase "leaves on the line" a standing joke, and, along with variants such as "the wrong type of snow", is seen by members of the public who are not familiar with the problem as an excuse for poor service.