Looking blindly through the MA regulations, I find:
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Section 1E....
A person operating a motorized scootershall have the right to use all public ways in the commonwealth except limited access or express state highways where signs specifically prohibiting scooters or bicycles have been posted, and shall be subject to all traffic laws and regulations of the commonwealth and the regulations contained in this section, except that: (1) a scooter operator shall keep to the right side of the road at all times, including when passing a motor vehicle which is moving in the travel lane of the way; and (2) the scooter shall be equipped with operational stop and turn signals so that the operator can keep both hands on the handlebars at all times. No person shall operate a motor scooter upon any way at any time after sunset or before sunrise.
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Hmm..
Separately, there is a distinctive class of over-20mph but under40 mph cycles.
to the above post, I rarely seen minimum-speed postings around MA.
Also, to MA visitors: forget about speed limits!