Driver reminder appliance

A driver's reminder appliance (DRA) is a manual switch in the driving cab of a passenger train. When operated it glows bright red and prevents the driver from being able to take power. It was introduced in the design and operation of United Kingdom passenger trains in the 1990s in response to a series of railway accidents where train drivers had passed a signal at danger when starting away from a station.

Use of the DRA is mandatory for drivers of British passenger trains and they are required by the Drivers' Rule Book to set it:

The DRA must only be reset:

A passenger train driver can easily become distracted by station duties and forget that the next signal is at danger. This signal might be hidden from view until the train is close to it and there is insufficient braking distance. The DRA helps prevent this problem because resetting the DRA is the last action the driver will take before powering away from the station.

The original DRA button was made out of plastic and broke after a while, which put the train out of service and caused delays. A manufacturer came up with a metal button which had a longer life.

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Wikipedia