I know how you feel, it took me a long time to get comfortable riding on the road for the same reasons...

I agree with the others that you should start by riding with a more experienced rider and wear clothing that makes you super-visible.

I think it's natural to be scared that a car coming up behind you may not see you since you can't see them, but statistically this is just not how cyclists typically get hit be cars. The most common cases are things that you can prevent by being alert, usually at intersections or when the cyclist is, say, riding the wrong way down the street. Be alert, be predictable, and getting a mirror to see what is coming up behind you may be a big help as well. It made me feel a lot more confident to be able to see cars behind me. There is a great mirror for mountain bikes by mirrorcycle.

Finally, you *should* be afraid of cars, they can kill or hurt you very badly. But if you are confident and safe the likelihood is really low; a healthy dose of fear will help you to stay alert and safe.

This article had a big impact on me...

Anne