I don't work with MA, but I don't believe anything like the 3/4ths rule would apply in a case like this. In a situation where one vehicle CLEARLY has the right of way over the other, and that vehicle would not normally be required to slow down, pause, or stop in any way, and the "yielding" vehicle pulls out in a manner that would force the first vehicle to slam on brakes, swerve, or otherwise take evasive action to avoid an accident, the "yielding" vehicle has failed to yield and will be assigned the majority of fault if an accident does occur. In some states (and MA may be one of them), the ROW vehicle may be assigned a small percentage of fault IF there is tangible evidence of extremely excessive speed, or if it can be shown that the ROW had the "last chance to avoid" the accident by taking evasive action, but did not. There, the 3/4 rule may come into play. However the PRIMARY cause of the accident will remain the failure to yield by the vehicle with the stop sign.