Reversing a roadway
You can use the Reverse Roadway tool to flip the two endpoints of a roadway, reversing the direction in which distances are measured.
For example, this diagram shows a roadway that is 20 miles long, with a sign positioned 4 miles from the start and another sign 13 miles from the start. The roadway is reversed. (Note that the arrows represent the direction in which distances are measured, not the direction of traffic or any particular compass direction.)
When the roadway is reversed, what was mile 0 becomes mile 20, and vice versa. So the sign that was 13 miles from the start is now 7 miles from the start, and the sign that was 4 miles from the start is now 16 miles from the start.