Why a public hearing for engine brake use?

Because you (town meeting) passed this:

On a motion duly made and seconded the town voted to amend the General By-laws by inserting a new Article LVIII, Engine Braking, as follows: No operator of a diesel truck shall use engine braking (also known as exhaust braking or Jake braking) while operating a vehicle on a public way, where such use is prohibited by the issuance of a Traffic Order by the Board of Selectmen after the holding of a noticed public hearing, in the Town of Templeton except in an emergency. Whoever violates this bylaw shall be punished by a fine of One Hundred Dollars ($100) for the first offense and Three Hundred Dollars ($300) for the second and subsequent offenses. The owner of the vehicle may be cited in lieu of the operator.

Passed by hand count of 50 yes and 47 no on May 15, 2019.