I have seen very few RM-type signs in my time here, but I think Mr Rothstein is more correct than I was, and in fact it is indeed RM 2222.srothstein wrote:I believe it is technically RM 2222.
And Mopac is a highway in Austin that was built along the MoPac railroad right of way. There is still an active track along the central median for part of the route of the highway. I believe it is also technically named Loop 1 and is a state highway.
I know this is only Wikipedia, but it will do for now.
It is a very fun road to drive.