If application is made for a location in a public way where no street railway tracks are located, and such way is widened under chapter eighty or eighty-two by an order declaring the widening to be necessary for public convenience for the purpose of granting such location of street railway tracks therein, a proportionate share of the expense of such widening may be assessed upon a company accepting a location in the way so widened; but the amount of such assessment, in addition to the amounts assessed on real estate, shall not exceed one half of the total cost of such widening.
Mass. Gen. Laws ch. 161, § 78