Train Protection & Warning System

The Train Protection & Warning System (TPWS) is a train protection system used throughout the British passenger main-line railway network, and in Victoria, Australia. According to the UK Rail Safety and Standards Board, the purpose of TPWS is to stop a train by automatically initiating a brake demand, where TPWS track equipment is fitted, if the train has: passed a signal at danger without authority; approached a signal at danger too fast; approached a reduction in permissible speed too fast; approached buffer stops too fast.

Source: Wikipedia — Train Protection & Warning System (CC BY-SA 4.0)