Any party receiving injury in his person or estate from any pole, or structure, or underground conduit or cable, or any attachment or appurtenance thereto within the highway limits may maintain an action for damages against the proprietor of the object causing such injury if such injury has been caused by the location of the object so as to interfere with the safe, free and convenient use of the highway, or by the negligent construction, operation or maintenance of such object; provided, however, that where a pole is unlicensed, the burden of proving that the object causing injury did not interfere with the safe, free and convenient use of the highway, or that such object was not negligently constructed, operated or maintained shall be upon the proprietor of such object. The provisions of this section shall not apply to actions for damages based upon injuries occurring prior to October 10, 1959.