In reply to MattDTC:
Generally none of the gates are locked - and from the piece on this that I wrote three years ago in my CalMerc days
http://caledonianmercury.com/2011/03/19/no-worries-but-plenty-of-potholes-o...
it seemed that the intention was that they wouldn't be locked - although the main focus in the piece was on the walking/cycling side of things, where unlocked access has by law to be maintained (unlike with traffic access).
Interesting to hear that Mike W has found one of the gates locked - I never have, in quite a lot of visits over the years. Since writing the 2011 piece I've been back there a couple of times, both times last June. The first was to park at the main track junction (with just one gate in play on the road to that point) for a Creag Mhor - Cam Chreag - Ben Challum round. Then a few weeks later a pal and I came back over the pass after a day on Stuchd an Lochain and the two Corbetts to the west. (Both were very good days, especially the Challum one.) On neither occasion was there any problem with the gates - although, as others have said, the state of the road on the zigzags south of the pass is now very poor, to the point of it hardly being worth the risk - I was in a Polo, which felt borderline in sturdiness terms. It's far from clear if any AA/RAC-type people, or even Lix Toll garage, would come out to fix a bepotholed or snowdrifted car on the hydro road.
Incidentally, on that Stuchd day we got there via the normal "Lawers road", and I kept an eye on the mileage - it was ten miles shorter (coming via Killin) on the hydro road, but whereas a few years ago the surface was good enough for that to convert to a 15-20 minute saving in time, now with all the first-gear pothole-weaving - and having to stop to open/close gates - I'd imagine the saving is ten minutes at most.