Initially the branch was operated by steam power, often a rail-motor, but the Croxley Green electric service commenced on 30th October 1922 (the electrification of the Rickmansworth branch being the last part of the project to be completed and electric trains did not run on that line until 26th September 1927). In October 1922, after electrification was complete, there were 25 trains running to and from Watford and in 1925, the Watford to Croxley Green local service, which had been weekdays only, was extended to cover Sundays. However, by the 1940's, the Sunday service was axed, along with the late evening workings.
In 1988, an attempt was made to revive the fortunes of the Croxley Green branch by running a twice hourly daytime service. However, Croxley Green station had fallen into a bad state of disrepair by this time with the single platform being boarded up and a temporary structure erected on either side of the line. Late in 1989 the rotting original platform was demolished, together with much of the original Watford West station structure. From January 1990 the Watford to Croxley service was reduced to one 7.00am return working from Watford Junction on weekdays only.
In 1996 a new road cut through the line just east of the Grand Union Canal bridge, severing the route between Watford West and Croxley Green. For a short time services were replaced by a bus and then by an occasional taxi. The branch was 'formally closed' in 2001.
Local residents will be aware of the resurrected proposals to link the Metropolitan Line from Croxley to Watford.
West of Watford - Watford Meropolitan & the L.M.S. Croxley Green and Rickmansworth branches by F.W. Goudie & Douglas Stuckey, published by Forge Books 1990. An invaluable source of information studded with photographs.
Underground History - North of Harrow and Wealdstone - Hywel Williams. A history of the line and several photos can be found here of the disused branch line showing it in its entire length. http://underground-history.co.uk/croxley.php
Wikepedia: Watford and Rickmansworth Railway. http://en.wikipedia.org/wiki/Watford_and_Rickmansworth_Railway