Par and ke upar can mean the same thing in many instances. Billi mez par hai and billi mez ke upar hai mean the same and both are grammatically sound.
But in this example of running on the road, using "ke upar" would be wrong. Only "par" would work.
Ke upar roughly translates to "above it". While "par" translates to "on it" quite closely. So you can see why, in some instances, both are interchangeable but many times they're not.