Lets take a look at "run over" and "over run", the the problem in German is the "um"
In different countries (and thanks for distinguishing between German-German and Austrian-German) the use of "um" is different, and it would be "überfahren" or "niederfahren" instead of "umfahren"
As others pointed out, it is a matter of stressing, but it's more complicated its a matter of semantics:
If you hurt a person with your car: the police would write "überfahren" (not to mention "angefahren")
an other tip:
If there is a traffic jam, radio will tell "umfahren Sie den Stau auf Ax" never ever somebody would think to crash into ...
so "umFahren" is in most cases "drive around", "try not to touch" seldom - and mostly bad speach "UMfahren"
Other example:
"ein problem umgehen" (avoid) - try to "UMgeh" a tree ... like run over a tree - or so
Last "bad" example:
"umschiffen" = "circumnavigate" (as I learned from a big internet translator, now), but, "schiffen" is a slang (Austria) for "peeing" ... try it ...
So if the tree is a Problem and 4 men coming from a bar are peeing at it, they say: this tree is a Problem we try "ihn um zu schiffen" or "wir "schiffen ihn um"
Edit: "umbauen" - for put something around, or change it