well you need to look at the project the right way, your whole home is like a soap bubble and the soundproofing is only as good as the weakest spot.
So you normally start with windows and doors first. Build these areas up to the highest STC possible and then if they are stronger then the walls that is when you attack the walls.
I know it can be a pain in the rear...but if you start with the walls most likely you will always look at the windows and doors as the culprit.
Now, there are a lot of variables that go into play with traffic noise based on the construction of the home, like raised foundation, lathe and plaster, distance to source etc etc...
So lets approach the problem methodically, you need to mimic what you see on commercial airplanes windows. 2 pieces of glass with the greatest airspace between them. The doors need to be as heavy as you can get and sealed air tight in the closed position.
once this has been done you will evaluate the reduction and determine if walls can be improved.
Feel free to contact me direct to discuss.
Randy S.
760-752-3030 ext 104