We live on an A road going out of a market town. We couldn't have afforded our house if it were just one road back as our 'suburb' of the town is probably the most desirable part of town to live. So we'd rather have our detached house with driveway on a-road in nice area, than terraced / on street parking away from a-road in not so desirable area. It all depends on personal preference I guess.
We didnt even consider the road when we purchased the house 9 years ago (not even married then, let alone thinking about kids), but now we have children we do sometimes worry about them running out into the road. However, we have a driveway with gates, we're in a 30 limit, and we're lucky that our A-road is, literally, the road to no-where (the wilds of the west country), so whilst there is a steady flow of traffic at rush hour, its fairly quiet rest of the time & pretty much dead at night.
To be honest, one of my friends lives on a road directly behind us (residential street), and she says the speed at which the cars shoot down her road (its a cul-de-sac) is really scary. And because they're residential, they have a false assumption that its safer than the main road. Our kids have had road safety drummed into them from a very young age.
OUr neighbours put their house on the market last year and sold within 3 weeks, so the a-road was certainly not an issue for them.
Re: road noise in the house, we have secondary glazing at the front (big bay window), and we do hear traffic noise from the back garden, but I find it rather reassuring! (grew up in a tiny village with only the sounds of tractors / cockerels / cows moo-ing and, to be honest, often felt totally isolated). Perhaps I'm just a townie girl at heart!
Anyway, waffly post, but I wouldnt let an a-road totally rule out a house purchase, there will always be someone who wants to buy a nicer house on a busy road than a less nice house on a quieter road (if you see what I mean?!)