I'm not sure... they used to, but I think they stopped them about 10-15 years ago due to concerns with too much traffic and noise. At the least, I know they no longer allow helicopter/airplane traffic below the rim, except for emergencies.
So...
Today my knees just hurt. Not exactly painful, more achy, but it was very unpleasant and I don't think I can bike home this afternoon. Any suggestions? Any that don't include drinking cod liver oil?
Or do I just need to expect that my knees will hurt when I bike more than three days a week, until I get better at this?