A Replacement Bus?

And what is a Replacement Bus?

We have many strange things in the UK which often puzzle our overseas visitors, one of which is our replacement bus service.

If there are difficulties with the train service, the train company may provide a bus service which replaces the train and will take you, on receipt of your train ticket, to your destination.

So, it is not a bus replacing a bus, although the idea would be widely welcomed by many UK residents!