Upset over Uber, natch. Shortly before 9 a.m., cab drivers blockaded the Mass. Ave. bridge into Cambridge. "Completely gridlocked traffic downtown," Christine Peterson reports.

About a half hour earlier, Bikeyface reported a salutary effect of the strike, when the cabbies were protesting in front of Cambridge City Hall:

Hey can I have a taxi protest block car traffic every AM commute? Felt so safe biking in on a nearly empty Mass Ave.

The scene in Central Square: