The risk of a SPAD▸ is small of course with TPWS▸ now able to solve most problems, but even a TPWS activation is taken reasonably seriously.
TPWS activation is a SPAD, as the TPWS grid is parallel to the signal, and only activates (and stops the train) as the train passes the red signal.
The risk of a SPAD is therefore very real, but because all signals are positioned with an emergency empty piece of track beyond them (**), a train can SPAD and be halted by TPWS before entering something like a single line.
Meanwhile every SPAD or SPAD & TPWS activation causes the driver and often signaller to be immediately removed from working (pending drug/alcohol test results), the incident is investigated and the record noted in the driver and signallers files. A very few incidents like this would end that persons career.
In addition, a record of the signal is made, as part of the ongoing assessment into signals that have multiple SPADs and what should be done to cure them.
(**) called the overlap (
TCB▸ ), or clearing point (ABS or Token/Tokenless block)