To pianoCM: Mile markers will typically start either 1) from a border (e.g., state line) or 2) the beginning of a road (one end or the other), and will continue by the mile (and sometimes even tenths) until reaching another border (e.g., state line) or end of the road.
As perhaps one of the most classic examples, the only mile marker "0" for U.S. 1 is at the very end of the line down in Key West. Stop and have a friend grab your photo there. You'll be about the 1 millionth visitor to do it!
In perhaps a more contemporary example, I-95 starts down in Miami with #1, and the last exit in Florida up north is #380, about 380 miles up the coast before reaching Georgia. The number then starts again with #1 just across the Georgia line, and continues north until #193, the last Georgia exit, and restarts again at #1 in North Carolina.