The permittee shall erect and maintain suitable timber barriers to confine earth from trenches or other excavations in order to encroach upon streets as little as possible. The permittee shall construct and maintain adequate and safe crossings over excavations and across streets under improvement to accommodate vehicular and pedestrian traffic at all street intersections. Vehicular crossings shall be constructed and maintained of plank, timbers, and blocking of adequate size to accommodate vehicular traffic safely. Decking shall be not less than four inches thick and shall be securely fastened together with heavy wire and staples. Pedestrian crossings shall consist of planking 3 inches thick, 12 inches wide and of adequate length, together with necessary blocking. The walk shall be not less than 3 feet in width and shall be provided with a railing as required by the Public Works Director.