I was suspecting that the answer would be based on the wording found in the Town of Arlington traffic code cited in post #5 by ZenBeam, to the effect that traffic turning on ANY green signal (including and arrow) must yield to other traffic, but according to the Mass. Drivers Manual at
http://www.mass.gov/rmv/dmanual/index.htm
On page 80 it says:
Green Arrow
A green arrow means you may make a “protected” turn in the direction of the
arrow. As long as a green arrow displays for your turning lane, pedestrians and
oncoming vehicles should be stopped for red lights. Look closely for signs saying
you may turn only on a green arrow.
Good luck and please keep us posted. Be careful out there.