A lot of British practice, apart from the 50hz, came mainly straight across the pond.
Certainly in the late 19th/early 20th century there was a lot of this. For example, those interested in telephone history here will know that the Automatic Telephone Manufacturing Co. was created to manufacture Strowger equipment under the patents which were held by Automatic Electric of Chicago.
But back on the subways, remember that while original cut-&-cover stretch of the Metropolitan Underground line was very British and designed for steam, by the time the "tube" lines (Piccadilly, Bakerloo, etc.) were built electric traction was to be the norm and not only were some of the systems influenced by U.S. practice of the time, even the funding was arranged by American financier Charles Yerkes.
I think there was probably more American influence in those early days than a little later, when we tended to drift away and "do our own thing" more.
