Pretty much all of the Cambridge and Somerville "squares" are really larger areas with nightmares of streets coming in and branching off at all sorts of random angles.

Left turn arrows tend to be eventually installed at the worst of the unprotected lefts. (Or left turns are just prohibited.) Locals just learn to expect a couple cars to do a left on red--and for another 2 or 3 to turn as soon as the light turns green.