Leaves on the line: A detailed explanation of the issue
We know that Metro customers get hugely frustrated by delays to Metro services, especially when that is caused by low rail adhesion as a result of leaf fall.
Below is a detailed examination of the issues and why the impact of autumn can hamper train services. It is a national problem that affects train companies across the UK.
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 the wheel from slipping, and braking distances extended.
If you’re a regular Metro 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 during autumn, particularly in the early morning and early evening.
The leaf mulch can also affect the operation of track circuits. Nexus has machinery to address this problem, which operates overnight on key sections of the network, spreading a special cleansing solution on the rails. Known as an RRV (Road Rail Vehicle), the specially adapted Ford Ranger truck travels around the network during the night when no trains are running, in order to treat rails ahead of the morning rush hour.
However, this can only reduce the impact of leaf mulch rather than eliminate it. The mulch is actually Teflon-like, and as hand-scrubbing could not remove all of it, the RRV is also fitted with mechanical rail scrubbers.
Nexus has also invested in Traction Gel Applicators – 5 of these units are strategically installed across the network in known areas of low rail adhesion. When a Metrocar passes over the unit, it automatically dispenses a solution called ‘traction gel’, which improves the friction between the wheel and rail interface.
Hand held applicators are also used by rapid response teams to address other areas of slipping and in an urgent situation where weather conditions change quickly, silica sand is manually applied to the rails.
The number of weeks this can continue for varies from year to year, depending on seasonal weather.
RE: Tyne and Wear Metro
''Leaf Fall Disruption Explained'' - Read at http://www.nexus.org.uk/metro/guide-metr...-explained