Barb, here in Silicon Valley (SF Bay Area, South Peninsula), we have lots and lots of bike lanes, including on pretty major roads. My morning commute is short, since I just ride to the train station where there's a shuttle for work that I ride.

However, my evening commute is about 10-13 miles depending on the path I want to take that day There are still bike paths, but since I make left turns at two of the major roads that I take, that means I go out into traffic to get into the left turn lanes. No path there. :P Honestly, if I could avoid the major roads and take a slightly longer, but less traffic road, I would. It's a matter of feeling safer and after riding 12 miles, another 1 mile isn't too bad. (at least if there are no hills )

Mel