Signal Passed at Danger - Passing Signals at danger - with Authority

with Authority

Signals form part of a complex system, and it is inevitable that they may go wrong. They are designed to fail safe, so that when problems occur the affected signal indicates danger (a notable exception to this being the Clapham Junction rail crash). To keep the network running, safety rules enable trains to pass signals that cannot be cleared to a proceed aspect. Provided that authority for the movement is obtained, a SPAD does not occur. Basically there are two types of signal, and they are treated differently:

• Automatic signals (those worked by the passage of trains) may not be passed at danger by the driver under his own authority.
• Controlled signals (those worked by the signaller to control the entry to junctions or conflicting movements) can only be passed at danger with the signaller's authority. The driver and signaller must both 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, proceeding with caution and travelling at a speed that enables him to stop short of any obstruction, and then obeying all other signals. If the signal is fitted with TPWS, he advises the driver of this. Then, if necessary the driver pushes the TPWS Trainstop Override button in his cab, sounds his horn, and proceeds cautiously through the section. If he reaches the next signal without finding an obstruction, he obeys its aspect, at which point he reverts to normal working.