New Adventures in Graph Theory

I have two offices for New Job. One at the university and one in another county. The office at the university is almost three miles from my house, and the other office is a little over 30 miles from my house.

This week is my first week full time, so I've been trying different routes too and from work. Now that I park at a different spot on campus, I need to figure out whether to take the city streets and arrive from the north or the big collector road and swoop around from the east. Google Maps says that one route is 9 minutes and the other is 13, but I don't believe it because there is too much margin of error when you're dealing with surface streets with tons of traffic lights.

Similarly with the distant office. It's a bit off the beaten path and not directly near the interstate. The question is whether I overshoot a bit on the interstate and backtrack just a little bit on the state road or whether I get off the interstate early and travel a longer distance on the state road. This seems to be a toss-up, as sometimes Google Maps prefers one route, and sometimes it suggests the other. (There is also the option of taking the state road the whole way, but that takes longer despite being a shorter distance.)