The second issue is that some people just won't buy such houses, regardless of the price. Let's say the comps in quieter neighborhoods are $500,000. You follow the procedure suggested by Mike and look at the variations between house prices in other somewhat nearby areas--busy street or not busy street. And you apply that same percentage reduction to the house you're asking about. Let's just say it's worth 10% less. (Just making that figure up.) So, the house you're interested in might be "worth" $450,000.
Problem is, if 20 people are interested in the house a few blocks away at $500,000, maybe only 15 would even consider your house, even at $450,000. Maybe they've got small children. Or pets. Maybe they're particularly sensitive to exhaust fumes. The point is: Your buyer pool will be smaller, too.
As TerritoryRE points out, those items will vary by town, city, and state. So there isn't a set number. Just recognize, though, that there's not only the lower value you're concerned about. There's also likely to be a smaller buyer pool.
Hope that helps.
Busy streets are not going anywhere so realize this isn't something your can ever fix or upgrade, and therefore, yes, when it is time for resale you will face this same marketing/value problem.
You have to look at comparable sales on similarly busy streets. Even if they are in different, but very comparable towns. Look for the most recent, ideally less than 90 days, SOLD homes (not active or pending sale) on street with similar noise and traffic influence to perform your analysis. That's what I do when I'm working as an Appraiser for the bank as well as when I'm working as a Realtor. These closed sales will give you the best indicator of current market value for homes on busy streets in that neighborhood.
If you buy properly now, chances are you will not lose your shirt if you need to sell in a few years. Yes, you are right, houses on busier streets usually tend to sell for less and take longer to sell than similar homes tucked away on quiet neighborhoods. Do the extra homework with the analysis NOW to ensure you BUY SMART.
If I can be of any help, please don't hesitate to reach out to me.