When I was on the sides of the lane I used to get buzzed by motorists or they would simply pass with inches to spare. This stopped when I was in the middle of the lane. I use my ears mirror and check my 6 when I feel it is appropriate.
Haven't had a problem doing this for over two years now. I'm not in what you'd call a bike friendly area either. Course the best plan is to avoid high traffic 60+ mph roads in the first place. If you train on em that is another story though.