Linear Path Optimization with Two Dependent Variables
You can consider the 1D-position of the 2 runners as one 2D-position. 
X-coordinate and Y-coordinate for respectively runners 1 and 2. So in your instance, the starting point is (0, 100).

Then all the goal points coordiantes can have a 2D-position in the same way, for instance (40, 70). Now the Travelling salesman problem has to be solved using the Tchebychev distance (infinite norm). I am pretty sure this is NP-complete.

A simple heuristic approach may be to always run to the next closest point (greedy nearest neighboor). Or you can either look for a more sophisticated one...