SPAD

Overview
A signal passed at danger (S.P.A.D.), known in the United States and Canada as running a red light,[1] is an event on the railway where a train passes a stop signal without authority.[2] Where colour light signals are in use, an S.P.A.D. occurs when a train passes a red signal without authority, and where semaphore signals are used, an S.P.A.D. occurs when a train passes a signal in the 'on' position without authority.

In the U.K, the alternative description signal passed at red is used where a signal changes to danger in front of a train due to either a technical fault or in an emergency, and although the train is being driven correctly it is unable to stop before passing the signal.

How to cause it
It takes a considerable distance to stop a train, and incidents of this type often involve a slight or very slight overrun of the signal, at low speed, because the driver has braked too late, often after sighting the signal too late.

In some situations, however, the driver is unaware that they have passed a signal at danger and so continues until a collision occurs, as in the Ladbroke Grove rail crash. In such cases it is up to the safety system (where fitted) to apply the brakes, or for the signaller to alert the driver.

Some of the causes are:
 * Misjudgement
 * Inattention
 * Distraction
 * Fatigue
 * Misreading of an adjacent signal due to line curvature, or sighting on one beyond[3]
 * Misunderstanding
 * Miscommunication[3]
 * Incomplete or lapsed route knowledge
 * Acute medical condition (medical emergency), such as a heart attack or stroke
 * Chronic medical condition, such as sleep apnea causing microsleep

Automatic train protection
Main article: Automatic train protection

Automatic train protection (ATP) is a much more advanced form of train stop which can regulate the speed of trains in many more situations other than at a stop signal. ATP supervises speed restrictions and distance to danger points. An ATP will also take into account the individual train characteristics such as brake performance. Thus, the ATP determines when brakes should be applied in order to stop the train before getting to the danger point. In the UK, only a small percentage of trains (First Great Western and Chiltern Railways) are fitted with this equipment.

Driver's reminder appliance
Main article: Driver's reminder appliance

The DRA is an inhibiting switch located on the driver's desk of United Kingdom passenger trains designed specifically to prevent 'starting away SPADs'. The driver is required to operate the DRA whenever the train is brought to a stand,[6] either after passing a signal displaying caution or at a signal displaying danger.

Once applied, the DRA displays a red light and prevents traction power from being taken.