25 Nov Reducing Risk from Leaves on the Line
In America, it is called the Fall and every Autumn the UK braces itself for a drop in punctuality as trees shed their leaves. The leaf film created by grinding dead leaves between a steel rail and steel wheel causes low adhesion, affecting punctuality and safety, and can affect the operation of track circuits. To manage the problem, the industry spends large sums every year controlling vegetation, cleaning the rail head and improving the ‘grip’ of wheels.
An increasingly popular way of improving grip is by spraying sand beneath the train wheels. This reduces problems with adhesion but the build-up of sand can also affect the operation of track circuits. To ensure that increased use of train sanders would improve safety overall, RSSB commissioned research project T1046 to compare the risks, and Rail Safety & Systems Assurance supported Lloyds Register Rail by performing the risk analysis.
Since adhesion problems are associated with particular routes and types of trains, the analysis used a spreadsheet-based version of RSSB’s Safety Risk Model to model risk on Strategic Route Sections (SRSs) of the rail network. To assess the risk accurately, the NMF Safety Module was adapted to model the increased probability of Signals Passed at Danger (SPADs) and Wrong Side Track Circuit Failures (WSTCFs) depending on the mix of trains and track circuits on each SRS.
The study found that the safety benefits from improved adhesion far outweigh any potential adverse safety outcomes associated with WSTCFs. The overall benefits from increased use of train sanders was estimated to be over £1 million per year and the project findings have been used to support the removal of restrictions on the type and number of sanders fitted to trains.