I second the rear-view mirror suggestion. If you're not doing so already, wear really bright colored jerseys. Yellow, orange, red, and bright pink are good, as well as bright prints. Dark colors make you nearly invisible to motorists, especially if you're riding at certain times of day. Add a rear red blinky light if you ride anytime near dusk. I also think that > 1 roadie riding together are more visible than just one lone rider, so if you have a friend you could ride with, you might feel more comfortable.
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow