You might have retinitis pigmentosa. It's a degerative eye disease that leads to tunnel vision and night blindness.
You need to go to an opthalmologist and get a field of vision test, which you will fail miserably if you have RP, and a retinal scan.
The good news is that if you're older and you've just noticed it there's a high chance that you won't go completely blind. The bad news is that it only gets worse and you probably will be legally blind at some point and will have to stop driving.
I was diagnosed with RP at 27 after noticing that I couldn't see near as well as my friends at night. I'm 41 now and probably shouldn't be driving.
The only thing you can do to slow it down is stay in good cardiovascular health and take ARED vitamans, preferably the ones with lower vitamin E content.
I seriously hope you don't have it. Feel free to PM me if you have any questions.