Signal passed at danger

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 (Great Western Railway and Chiltern Railways) are fitted with this equipment.

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,[9] 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.

On the London Underground (for example), mechanical train stops are fitted beside the track at signals to stop a train, should an S.P.A.D occur.

Train stops are also installed on main line railways in places where tripcock equipped trains run in extensive tunnels, such as the on the Northern City Line where the Automatic warning system and Train Protection & Warning System are not fitted.

On the UK mainline, AWS consists of an on-board receiver/timer connected to the emergency braking system of a train, and magnets located in the center of the track. At each AWS site, a permanent magnet arms the system and an electromagnet connected to the green signal lamp disarms the system and a confirming chime is provided to the driver. If the receiver does not disarm within one second after arming, a warning tone sounds at the driver's desk and if it is not cancelled by the driver, the emergency brakes will be activated. A visual indication remains set to remind the driver that they have passed a restrictive signal aspect.

On the UK mainline, TPWS consists of an on-board receiver/timer connected to the emergency braking system of a train, and radio frequency transmitter loops located on the track. The 'Overspeed Sensor System' pair of loops is located on the approach to the signal, and will activate the train's emergency brake if it approaches faster than the 'trigger speed' when the signal is at danger. The 'Train Stop System' pair of loops is located at the signal, and will activate the emergency brake if the train passes over them at any speed when the signal is at danger.

TPWS has proved to be an effective system in the UK, and has prevented several significant collisions. However, its deployment is not universal; only those signals where the risk of collision is considered to be significant are fitted with it.

At certain junctions, especially where if the signal protecting the junction was passed at danger a side collision is likely to result, then flank protection[10] may be used. Derailers and/or facing points beyond the signal protecting the junction will be set in such a position to allow a safe overlap if the signal was passed without authority. This effectively removes the chance of a side-impact collision as the train would be diverted in a parallel path to the approaching train.

SPAD indicator

Prior to the introduction of TPWS in the UK, "SPAD indicators" were introduced at 'high risk' locations (for example: the entry to a single track section of line). Consisting of three red lamps, they are placed beyond the protecting stop signal and are normally unlit. If a driver passes the signal at 'danger', the top and bottom lamps flash red and the centre lamp is lit continuously. Whenever a SPAD indicator activates, all drivers who observe it are required to stop immediately, even if they can see that the signal pertaining to their own train is showing a proceed aspect. Since the introduction of TPWS, provision of new SPAD indicators has become less common.

Once the train has been brought to a stand at a signal which is at danger, the driver should attempt to contact the signaller. If the signal cannot be cleared then the driver must obtain the signaller's authority to pass it at danger. Methods for contacting the signaller may include GSM-R cab radio, signal post telephone or mobile phone.

The signaller can authorise a driver to pass a signal at danger when:[14]

• The signal is defective or disconnected
• The signal cannot be cleared because signalling or level crossing equipment has failed
• The signal is to be passed at danger for shunting purposes
• The signal cannot be cleared because a train or movement which has reversed is then required to start from beyond that signal
• An electric train is to pass the signal protecting an isolated section and proceed towards the limiting point
• A train has been accepted using restricted acceptance because the line is clear only up to the home signal of the next signal box and the section signal cannot be cleared
• In an emergency, and then only when authorised by the signal box supervisor or Operations Control, so that a train carrying passengers can enter an occupied section to use a station platform
• An engineering train is to move towards a possession, or leave a line under possession at an intermediate point
• A train is to pass the signal protecting engineering work to gain access to a station where the train is required to start back, or a line under single line working, or a siding
• The line is to be examined to check that it is clear
• A train is to proceed at caution through an absolute block section from the signal box in rear when a failed train has been removed
• A train is to enter the section after a train or vehicle that has proceeded without authority has been removed, or the front portion of a divided train has passed through the section
• A train is to enter the section to assist a failed train, evacuate passengers from a failed train, remove a portion of a divided train, or remove a train or vehicles that have proceeded without authority
• Single line working applies
• Working by pilotman or modified working applies

The driver and signaller must come to a clear understanding, and ensure they agree about how it is to be done. In the UK the signaller tells the driver of a specific train to pass a specific signal at danger, proceed with caution and travel at a speed that enables him to stop short of any obstruction, and then obey all other signals. If the signal is fitted with TPWS, the driver resets the Driver Reminder Appliance, pushes the TPWS Trainstop Override button in the cab, and proceeds cautiously through the section. If the train reaches the next signal without finding an obstruction, they must obey its aspect, at which point they can revert to normal working.

If contact with the signaller cannot be made then the driver must not move the train, unless it is standing at one of the following signals:

• An Intermediate Block Home signal
• A signal controlled from a signal box that is closed
• An automatic signal where local instructions permit it, e.g. signals within tunnels on the Northern City Line.

After passing a signal at danger under his own authority, the driver must stop at the next signal (even if it is showing a proceed aspect) and inform the signaller of what they have done.