Section 36. The commonwealth shall be liable for injuries sustained by persons while traveling on any boulevard maintained by the division under authority of the preceding section, if the same are caused by defects within the limits of the constructed traveled roadway, in the manner and subject to the limitations, conditions and restrictions specified in sections fifteen, eighteen and nineteen of chapter eighty-four, except that the commonwealth shall not be liable for injury sustained because of the want of a railing in or upon any boulevard, or for injury sustained upon the sidewalk of a boulevard or during the construction, reconstruction or repair of such boulevard. All sums recovered against said division under the foregoing provisions, together with any costs of suit and counsel fees, expenses and interest, shall be deemed expenses of care and maintenance of boulevards.