How unionized is Boston?
I imagine that virtually all the subcontractors on the Big Dig were signatory with a local union and that the overall project had a PLA (Project Labor Agreement) calling for signatory contractors in exchange for a no-strike/no-stoppage agreement by the local trades council.
Perhaps someone in local Boston construction market knows for sure, but that was my impression.
That being said, the quality of union and non-union work in heavy and commercial construction work is not divided up along union versus non-union lines. Both the signatory firms and the non-signatory firms have a small percentage of workmanship problems in certain cases. The project to project culture is more in control of the build quality even from the same firms.
The entire project was built by unions - whose motto is “Build it poorly now and we can rebuild it poorly in just a few years! Go AFL-CIO!”
As I recall, in those trades, very unionized. I grew up in MA and have observed to relatives there that the Big Dig seems mostly like a union "Let's get rich and retire" boondoggle.