Armagh and the block system
On 12 June 1889 a Sunday-school excursion train near Armagh, in Ireland, stopped on a steep incline when the engine could not climb it. The crew decided to divide the train and take the front carriages on to the next station. The rear section was left behind with its wheels blocked by stones, but when the engine began to move, the stones slipped and the rear carriages ran back down the hill, where they collided with a following train. Eighty people died, many of them children.
The train had a simple brake that worked only when the driver applied it and which on the rear carriages did not operate automatically when they were detached. There was no rule that stopped one train from entering a section while another was still in it.
The Regulation of Railways Act
Parliament responded the same year with the Regulation of Railways Act 1889. It required all passenger trains in Britain to have continuous automatic brakes and railway companies to adopt the block system, under which a section of track may hold only one train at a time, with signals and points interlocked so that conflicting movements are impossible. These ideas became the basis of railway safety in many countries.