The trucking industry views plans by Tesla Inc. to develop an electric semi-tractor with a mix of skepticism and trepidation. At first glance, the hurdles the Palo Alto, Calif., automaker must overcome to launch an electric big rig appear huge. There is almost no market for electric trucks now. The highway charging network for heavy-duty vehicles does not exist. The weight of the batteries that provide power to a semi-tractor eat into precious cargo load capacity. Diesel fuel is cheap, keeping a lid on the cost of operating a conventional truck.