Semi trucks are a fixture on the world's highways, transporting a significant portion of the world's cargo — and that's leading to a rash of innovation in the space that mirrors what's happening in the automotive world. Self-driving trucks, electric powertrains; you name it, someone's working on it. Siemens is working on something interesting, too: a pantograph system that would let big rigs drive for miles without sipping a single drop of diesel.

The system, which Siemens calls an "eHighway," is being tested on a public road for the first time in Sweden in partnership with Volkswagen-owned Scania. It uses pantographs mounted on top of each truck, which can deploy and retract at speeds of up to 90 km/h (56 mph), to connect to an overhead wire system on certain segments of the highway; when attached, the truck's diesel powertrain can shut off and run on electricity alone. In segments without wires, the truck operates on fuel just like any other. Some public transit authorities around the world use similar systems on networks of buses and regional railways.

The system is only deployed on a 2-kilometer (1.2-mile) stretch of road right now, but Siemens is planning a second trial in California next year with Volvo Trucks. It's probably not practical for private vehicles — who wants a pantograph mounted to their roof? — but for emissions-belching big rigs, it's an interesting solution.

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