I'm not sure I really buy that; Massachusetts is bigger than just Boston (which has plenty of "fast" roads, e.g. Storrow Drive) and has roads of all shapes, speeds and sizes, including a great deal of "sprawl" in the suburbs (~6X the population of urban Boston/Somerville/Cambridge) and half the state by land area worth of "exurb farming country."

IME, driving in Boston seems to involve the most potentially-deadly situations given the number of pedestrians and cyclists. Twice in the past year driving on Comm Ave I've had to swerve into the left lane to avoid hitting one, first a cyclist who blasted through a red light at an intersection, then a woman who, on her phone, dressed all in black at night, stepped directly in front of me in 30mph traffic, half a double-length block from the nearest crosswalk or stoplight.

If I had glanced at my phone, adjusted the radio, talked to a passenger or otherwise had less-than-instant reflexes in either of those moments those people might well be dead, or else severely injured. (Also, I and others could've been injured or worse if I'd swerved into another car).