Joshua Hart has done an interesting study in Bristol, which shows that people who live in streets with more traffic visit their neighbours less.
This is interesting, but what cannot directly say is "living on a busy street makes you friendless". Why? Because one possible hypothesis is that friendless people choose to live on busy roads. Houses on/by busy roads cost less, they are often divided into flats and may have higher turnover. And it is that turnover that may effect things. What would be interesting would be take one of the roads in the study -such as Muller Road- block it off to car traffic for a month, and see if that leads to increased neighbourliness. Having seen the consequences of Cotham Brow being closed to traffic, and how much quieter the whole area became, the results may be surprising.
Another possible hypothesis -though it seems even more unlikely is this: if a street forms a strong community, does its traffic decrease? mu