were there roads or flyovers on the sanandreas fault??????

Answer 1

California & surrounding states became heavily populated with millions of people, their homes, roads, shopping malls, etc. long before scientists figured out the San Andreas Fault was down there.

Just like the City of New York was built long before people figured out that the Atlantic Ocean would send a big tidal wave there every 100 years or so.

We have metropolises all over the world that are threatened by various perioidic natural disasters.

Answer 2

There are plenty of roads that cross the San Andreas fault. Interstate 10 crosses it, I-5 runs parallel to it (as does US 101), California 166, and many smaller roads.
Planes fly over it every day. There's no reason not to.