The City maintains a list of all streets that are so called 'private ways'. Many residents don't realize their street (or portion of) is not an accepted street. Developers can extend a street or create a street without making it a public way, and often do so to avoid having to comply with the requirements to make it a street the city would 'accept'. So you'll see on that portion of Wyeth it is different than the rest of the street, namely no sidewalks. That is the first tell tale sign. While the city still plows and cleans the street (many cities don't) we are not allowed by law to enforce the rules that apply to the public way because it's not a public way. The only thing we are able to do is enforce if it's preventing access for public safety. There is quite a bit of information on the internet that speaks to the topic consistent with what is above. This article in particular is helpful and thorough.

http://archive.boston.com/news/local/massachusetts/articles/2008/02/10/private_ways_public_access/?page=2