You're not wrong Trev. There were other similar systems as well (Lorraine, etc.). The main problem was that a stud could remain live and would cause problems for other road users, They did try metal brushes under the cars which, if they hit a live stud, would cause a short-circuit (presumably throwing a breaker).
Mechanical types, which linked each stud - so only the stud under the leading skate was raised - were tried but the usual problems of wear and tear and the detritus from horse-drawn traffic meant that system did not prevail. The trailing skate pressed the stud down and raised the next in front. The skates were extremely long. This was the Anderson system tried out in Leeds.
Interesting stuff!
Mick
I thought Alyn's photo was an actual installation of the real thing! (I still think it is).