Is it a bus? Is it a tram? Is it a train?
Something of each, in fact—and something new, as well.
Developed in Dresden, the AutoTram is a fully electric, zero-emission light-train on wheels. The new bit is how the three-segmented vehicle is powered. Rather than running on a single charge like an electric car, it goes between charging stops, where it gets 30-second jolts of energy before continuing on.
Ulrich Potthoff, head of the transport department at the Fraunhofer Institute, which is developing the concept, says the aim is to have the dexterity and low costs of a bus, without the noise and fumes. "We wanted it to be flexible and rather cheap like a bus system—less expensive than light rail. One way we achieve that is not to have any overhead line, or rails."
During the first demonstration phase of the project, Fraunhofer packed the AutoTram with technology—fuel cells, flywheels, batteries—seeing what combination would work best. The challenge was to strike a balance between the power needed for acceleration, and the energy storage required for decent distances.
For the full prototype, now being developed, Potthoff’s team has hit upon a mix of a battery and "super-capacitors" which can store large amounts of power for short periods. The AutoTram can travel up to 1.2 miles before it needs to be recharged, locking itself into a dock beneath a passenger platform where it gets a burst of up to 700 volts. Potthoff says 1.2 miles should be plenty in most cities (the average distance between stops in Germany is about 0.3 miles). But just in case something goes wrong, there is a backup diesel-based electric generator.
Potthoff says it would have been possible to use lithium-ion batteries, charging up before and after trips. But the cons outweigh the pros: lithium-ion units are heavy and relatively expensive, and there is a limit to how much you can keep recharging them. He says 1,000 cycles is probably the upper end. "I’m not saying you can recharge our system an infinite number of times. But it is many, many more times than with a lithium battery."
Fraunhofer is a private for-profit research institute that sells technology to companies who bring products to market. Potthoff says several European companies have shown interest in AutoTram—probably for eventual export to the developing world.
"I think this is most useful in countries which only have diesel buses and want to do something new with transportation. They are calculating that overhead lines and infrastructure is very expensive compared to our system."
When it’s finalized next year, the AutoTram will likely have lifecycle costs 30 to 50 percent cheaper than light rail, but be appreciably more expensive than diesel buses. "If it’s not subsidized for environmental reasons, you would not be able to calculate in an equal way," Potthoff says.
The system could, though, be attractive to European cities that want to prettify certain historic areas. Even if AutoTram system is more expensive than buses, cities like Milan and Dresden might be prepared to pay a premium to do away with ugly overhead lines and screechy tram lines, in favor of a quiet, clean, and wireless alternative.