I used to ride on a similar road. 45mph with no shoulder, and the traffic would come in sourts as they caught the light a quarter mile back, like cattle being herded. I swear they would buzz me purposely, no matter what position I took in the lane. I never really found a solution, my job there ended not long after I started bike commuting so the problem was over. But it did seem that these people thought I was invading their space so they would purposely pass me very closely to convey their frustration.
Did I mention that I hate people?