OBER-RAMSTADT, Germany — On a highway south of Frankfurt recently, Thomas Schmieder maneuvered his Scania tractor-trailer and its load of house paint into the far right lane. Then he flicked a switch you won’t find on most truck dashboards.Outside the cab a contraption started to unfold from the roof, looking like a clothes-drying rack with an upside-down sled welded to the top. As Mr. Schmieder continued driving, a video display showed the metal skids rising up and pushing gently against wires running overhead.The cab became very quiet as the diesel engine cut out and electric motors took over. …
