The routes are categorized by the altitudes at which they are typically flown (1500 AGL or less for low level routes, 1500AGL or above for higher altitude routes, and then whether they're flown under VFR or IFR). The fun ones to look for are VR routes with 4 digit codes (signifiying 1500AGL or less).
Here's a youtube video of a r/w flight in an F/A-18 along VR-1251, just north of Shelter Cove in Northern California: http://www.youtube.com/watch?v=uZrTVKaPjDg
You can find the route on skyvector right here. Look for Punta Gorda and you'll see where VR-1251 hits the shoreline. That's where the video kicks off.
We have B1's and F/A-18's flying along several MTR's in Socal on PE, too. The flight profiles look pretty much like that video. Later research showed a speed limit of 480KIAS on MTR's. Oops.
