Unwarranted fear: how do we get our kids to avoid running on the road the FIRST time?

Ok I want to believe that as parents we all have at least one fear that's irrational. This is what I keep wondering: I keep seeing kids my daughter's age or so toddling behind their parents on walks, etc. and the parents seem so confident their kid won't go onto the road. I'm not inept at eaching or trainning my daughter - she listens very well at all timea sn dit doesn't take much to get her to follow direction - BUT, that being said, it typically will take her one *test* of the rule before she fully listens. I'm terrified to even be on my front lawn with her in case she runs onto the road when a car zooms past. It's a catch 22. I can't teach her NOT to unless I expose her to the opportunity to play out front or walk near the side walk so I can show her what NOT to do, yet i also don't believe that the first time I ever point to the road and say, "we don't ever go onto the road unless we're holding mommy or daddy's hand" that she's going to listen 100% without trying it at some point to see if she gets heck for it. and I'm dreading that *test*! how did other parent handle this? Do you find in most cases kids just instinctively know not to test this one? Like i say my kid usually only needs to be told once before she totally stops a bad behavior, but that ONE time almost always occurs. and in this case one time might be all it takes. but I can't know if I can trust her unless I let go of the iron grip I always have on her wrist around the road, and see if she ever makes a break for it or see if she follows directions properly. i know I'm over thinking this, but seriously, what happens in most cases? ( daughter is now 23 mo)