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Signal passed at danger
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Signal passed at danger
A signal passed at danger (SPAD) is an event on a railway where a train passes a stop signal without authority. This is also known as running a red, in the United States as a stop signal overrun (SSO) and in Canada as passing a stop signal. SPAD is defined by Directive 2014/88/EU as any occasion when any part of a train proceeds beyond its authorised movement. Unauthorised movement means to pass either:
The name derives from red colour light signals and horizontal semaphore signals in the United Kingdom, which are said to be at danger when they indicate that trains must stop (also known as the signal being on). This terminology is not used in North America where not all red signals indicate stop. In the UK, a signal passed at red (SPAR) is used where a signal changes to red directly in front of a train, due to a fault or emergency, meaning it is impossible to stop before the signal.
The high inertia of trains, and the low adhesion between the wheels and track, means it takes a long distance for the train brakes to stop a train. SPADs are most commonly a small overrun of the signal (instead of a long overrun), because the driver has braked too late. The safety consequences for these types of SPADs may be minor. On the other hand, some SPADs involve the driver being unaware they have passed a signal at danger and continue until notified by network controllers, or a collision occurs, as in the Ladbroke Grove rail crash.
The causes and prevention of SPADs is actively researched. Common causes of SPADs include:
Automatic train protection (ATP) is a system that can limit train speed in situations other than at a signal set at danger. ATP can supervise speed restrictions and distance to danger points. It can also take into account individual train characteristics such as brake performance etc. Therefore ATP can determine when brakes should be applied in order to stop the train before passing a signal at danger. Presently, In the UK, only a small percentage of trains (Great Western Railway and Chiltern Railways) are fitted with this equipment.
The driver's reminder appliance (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, 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 until the DRA is manually cancelled by the driver.
Whilst the ideal safety system would prevent a SPAD from occurring, most equipment in current use does not stop the train before it has passed the danger signal. However, provided that the train stops within the designated overlap beyond that signal, a collision should not occur.
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Signal passed at danger AI simulator
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Signal passed at danger
A signal passed at danger (SPAD) is an event on a railway where a train passes a stop signal without authority. This is also known as running a red, in the United States as a stop signal overrun (SSO) and in Canada as passing a stop signal. SPAD is defined by Directive 2014/88/EU as any occasion when any part of a train proceeds beyond its authorised movement. Unauthorised movement means to pass either:
The name derives from red colour light signals and horizontal semaphore signals in the United Kingdom, which are said to be at danger when they indicate that trains must stop (also known as the signal being on). This terminology is not used in North America where not all red signals indicate stop. In the UK, a signal passed at red (SPAR) is used where a signal changes to red directly in front of a train, due to a fault or emergency, meaning it is impossible to stop before the signal.
The high inertia of trains, and the low adhesion between the wheels and track, means it takes a long distance for the train brakes to stop a train. SPADs are most commonly a small overrun of the signal (instead of a long overrun), because the driver has braked too late. The safety consequences for these types of SPADs may be minor. On the other hand, some SPADs involve the driver being unaware they have passed a signal at danger and continue until notified by network controllers, or a collision occurs, as in the Ladbroke Grove rail crash.
The causes and prevention of SPADs is actively researched. Common causes of SPADs include:
Automatic train protection (ATP) is a system that can limit train speed in situations other than at a signal set at danger. ATP can supervise speed restrictions and distance to danger points. It can also take into account individual train characteristics such as brake performance etc. Therefore ATP can determine when brakes should be applied in order to stop the train before passing a signal at danger. Presently, In the UK, only a small percentage of trains (Great Western Railway and Chiltern Railways) are fitted with this equipment.
The driver's reminder appliance (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, 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 until the DRA is manually cancelled by the driver.
Whilst the ideal safety system would prevent a SPAD from occurring, most equipment in current use does not stop the train before it has passed the danger signal. However, provided that the train stops within the designated overlap beyond that signal, a collision should not occur.
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