Leaf fall disruption

Leaf fall causes a problem called low rail adhesion. This is a problem that affects train companies right across the world.

When leaves fall on to the line, particularly in damp or wet weather, the rolling action of passing train wheels compresses them, causing a greasy ‘mulch’ to cover the top of 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 the steel train wheels and the rails. Acceleration must be reduced to prevent the wheel from slipping and braking distances need to be extended.

Because of their lightweight construction and rapid acceleration, Metro trains are particularly susceptible to low rail adhesion conditions.  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.

The leaf mulch can also affect the operation of signalling track circuits.

• Extra training and mentoring is provided for less experienced Metro drivers to deal with low rail adhesion.
• Tree surgery and vegetation clearance is carried out in to reduce the level of leaf fall in Metro corridors during the autumn months.
• Special vehicles operate on the track in the early hours before trains come into service on key sections of the network, spreading a special cleansing solution on the rails.
• Nexus uses static Traction Gel Applicators – Five of these units are strategically installed across the network in known areas of low rail adhesion.  These units continually dispense a solution called ‘traction gel’, which is spread along the rails by Metro trains and improves the friction between the wheel and rail interface.
• Handheld 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.
• Quicker reporting of low rail adhesion through the Metro Control Room and daily reviews of specific incidents to target problem areas on the Metro system including proactive monitoring of weather conditions to determine the likely effect on rail conditions for drivers.