And the answer is....
As Jason said, the farm-to-market road system was established to ensure farmers all-weather access to markets for their crops. In a nutshell, the government provides additional funding for the maintenance of FM roads above and beyond whatever resources are available to the local authorities for that purpose. Altho a few of the midwestern states have done away with the township government format, for the most part the townships are responsible for maintenance of our beloved grid backroads. And the resources available to these townships varies wildly depending on the taxable base, i.e. population. In the really rural townships, some of which don't even boast a small village in their district, those extra funds can cover an annual oil-and-chip top-dressing and a few shovelsful of asphalt road patch.
Unfortunately for us, there's often no way to tell if you're on a FM road or one of their lesser brethren. You just gotta know. If you ARE on one, if nothing else, there's a good chance it's going to go somewhere and not dead-end or go unexpectedly mud on you.
And whoa!! 70-75 mph posted limits???? Clearly Texas FM roads are a whole 'nother species than the Illinois variety. About the only signs you see posted on ours are "Narrow Bridge" and seasonal weight limits. No need, I guess, to post a speed limit on a road that will tear vital components from your vehicle at anything over 60mph.
I am one of those spoiled country folks fortunate enough to have a farm-to-market road out front. It's still just an unstriped, move-over-to-meet, single lane country road, only a little wider, a lot smoother, gets fresh oil-and-chip every year and an occasional full regrade and resurface. It's also the first road plowed after the snow. Sweet.
