RSSB2687 - T1144 - Braking in snow conditions

Following the derailment of a container-carrying train at Carr Bridge on 4th January 2010, the relevance of the rule book instructions for running brake tests in snow was questioned.

The incident at Carr Bridge was preceded by a similar runaway incident at Carstairs on 22nd December 2009.

The rule book at the time of these incidents (GERT8000 TW1) stated the following instructions when encountering fallen snow : "You must make a full-service application of the automatic brake every three to five minutes and make sure that the speed of your train is reduced by at least 10 mph because of the application.

If driving a locomotive-hauled train, you can extend this interval when: the train is climbing a steep-rising gradient, and the train might be brought to a complete stand as a result of using the brake" Whilst the latest amendment to the rule book, in force from December 2013, are less descriptive and mentions the duty of the operators : "When snow is falling, or fallen snow is being disturbed by the passage of trains, you must carry out running brake tests as frequently as necessary to make sure that the automatic brake is operating effectively.

You must also carry out any other train operating company instructions." The practice within operators following the change has been to maintain the status quo stated in the old requirements.

These instructions were created at a time when most of braking systems used in GB utilised friction braking (brake blocks and brake pads).

For such systems it was necessary to both prevent a build-up of ice and snow between the friction element and the wheel or brake disc, and to prevent moisture seeping into the friction material then subsequently freezing and adversely affecting its friction properties.

The instructions for a running brake test were intended to not only test the brakes, but to additionally generate sufficient heat in the brake system to both melt any forming ice and snow, and to dry out any water within the friction material, so preventing the development of issues.

Train braking systems have advanced and modern rolling stock may now use a combination of regenerative, rheostatic or retarder braking, in addition to friction braking.

Such systems do not rely on contact between the friction elements and wheel / brake disc to slow the train and may therefore not be susceptible to loss of performance during snow conditions or may be susceptible in different ways which are not addressed by running brake tests.

Further, such systems may render the past (current) practice of running brake tests ineffective at dealing with snow conditions, by reducing the heat generated in the friction brake system.

Through industry engagement it is seen that many operators still adopt practices that are consistent with the old requirements.