Short answer - it depends. Time of day, proximity to the street, and part of the road all play a role. Parts with major crossings (say Cochituate rd and Old connecticut path, as well as rt 20 intersection) will be busier than the rest. Morning and evening rush hour will be rather busy - many cars on the road moving rather slow. If you have small children it might be a good idea to have a fenced in yard.
If you are concerned with driving (how long will it take, and how easy / hard will it be to merge) - again, it'll be slower during rush hour, but easy to merge. Other drivers are usually mindful of cars trying to get out of the driveway, or turn from a side street.
If you compare Cochituate rd to others, Mass Pike will be the busiest, rt 9 second busy, and Cochituate is similar to rt 30, or even less busy than that. Hope this helps, let me know if you have other questions about the area.