Third and fourth rail systems are largely deprecated due to the dangers to workers.

Overhead lines are safer, but require adaptation of the formation at stations, bridges and tunnels. This is the sticking point on the Great Western main line, as the clearances were already lower before the trackbed had been raised in the 80s to give the HSTs a smoother ride, leaving no room for OHLE without expensive works.

Batteries are a compromise, and could be the permanent solution for shorter routes.