Fifty miles per gallon. For a car, it sounds impressive. For a bus, if it can be achieved, it's astronomical.

Adura Systems claims it can pull off that feat with its MESA power train for buses that the company hopes to commercially release next year. The system consists of up to modules holding lithium-ion batteries or ultracapacitors, a gas generator for recharging the batteries while driving and a complex array of software and circuit boards that juggle electrical loads to maximize performance and drive time.

The electronic system, for instance, can detect which battery packs are nearly depleted and which are full, as well as which batteries are running hot. By massaging and controlling the system, the bus can go 100 miles or more and get 50 miles a gallon, according to CEO Marv Bush.

Most buses get about three to five miles a gallon. Diesel hybrid buses have brought that up a bit, but nowhere near the 50 mile per gallon level.

Adura will first try to release the product commercially in China, but also aim for contracts in the U.S. Approximately 175,000 new buses hit the road in China ever year compared to only 5,000 in the U.S., he said. China also has 40 bus companies compared to four in the U.S.

"China has a huge image problem with emissions and they don't want that reputation anymore," he said. "They also don't want to be dependent on fuel imports."

One of the keys to the system is its modularity. The battery packs, which can hold up to 22 kilowatt hours of power each, slide in on rails. A bus can go out with ten, or three. A maintenance staff can juggle the type of capacity to better fit the local topography. Instead of ten battery packs, a bus can be loaded with seven battery packs and three modules loaded with ultracapacitors, which can provide acceleration. Technically, buses based on the MESA will be serial hybrids, similar to the Chevy Volt, because they will drive on electricity but use a gas generator to recharge.

"The difference between an all-electric and a series hybrid is that a series has a generator," he said.

Different battery chemistries - lithium-ion manganese in one bay followed by lithium phosphate -- is also doable. You could even install a fuel cell. (The battery packs use cylindrical instead of prismatic cells. Cylindricals are cheaper and constitute the bulk of volume production.)

Buses and heavy trucks aren't nearly as exciting as sports cars, but some believe that tackling heavy vehicles first could have a greater impact on emissions. The engines are dirtier, after all, and they get lower mileage.

Batteries and electrification also fit buses better in many ways. Buses drive in set patterns close to home like draft horses and are maintained in big garages with spare batteries. Thus, bus drivers don't have to worry about third parties building charging stations – a city can build a few in a central local on its own.  Battery swaps also work because the single agency owns all of the batteries and buses, and it trains the mechanics how to swap them.

But the cost? Bush claims that his drive train will cost $155,000 compared to $30,000 to $45,000 for a gas drive train in china or a $75,000 drive train in the U.S. Lower maintenance and fuel costs, however, will mean a two-year payback.

Though $155,000 seems awfully cheap for lithium-ion battery packs. Proterra, a competing company that sells a completely electric bus, says it can undercut the total cost of ownership of a regular bus by around $310,000 over a twelve-year period. Adura says it will save municipalities around $800,000 over an eight-year period.

Proterra also has completed prototype buses. Adura has a 1/10th scale mock up.