It always causes delay. If there is an act of vandalism, as there are all too frequently, every time it also causes delay. Of the many, many things that happen on a railway, they almost all, with very few exceptions, lead to both safety exposure and to delay. If you eliminate the things that go wrong, if you reduce the things that go wrong, you end up with a more reliable railway, but by definition you have to end up with a safer railway. The safest railway I know is one where every train runs on time.
Every train receives green signals.
There is no possibility of SPADs because there are green signals. Nothing has gone wrong. The system is working properly. I have said the two are virtually indistinguishable for an operational railway. We cannot deliver improved performance unless we deliver improved safety.