Texas has a four tier system: Interstates, Federal (US) numbered, State Highways (ex. TX 149), and Farm to Market Roads. The Farm to Market roads are usually indicated FM (example FM 1649). The number of digits is only significant in one way: the smaller the number the earlier it was added to the system. Smaller numbers sometimes mean tighter curves as the earlier FM roads generally followed the old county and local roads. However, we frequently choose FM roads and find most of them quite acceptable--just not as fast. Texas state roads are usually very good.