the combined frequency of the electric trains from south hampstead to watford was thus about every five minutes, and the through bakerloo trains were additional to this. this very substantial operation (compared to later years) was behind the installation of the pioneer automated signalling system in 1933, which lasted until 1988 when replaced by a conventional system, by which time services were substantially reduced. the 1933 signalling system had allowed scheduled headways of two minutes on the route.