I know what you mean about colds/flu and biking. I always (now that I have the option) drive 1 day more than I think I need when recovering from a cold.

And it serves as a good reminder of why I prefer to ride: I work on a military base, and it's almost exactly 5 miles from my driveway to my office. If I drive, it takes 12 minutes to get to the traffic, then 20-30 minutes sitting in traffic waiting to get on the base.

When I bike, it's almost exactly 30 mins door to door, and traffic doesn't affect me.