It specifically said city driving. The system uses brake regenerative technology as well as the hydraulic accumulators. It would be easy to greatly improve mileage in stop and go city driving especially if you could turn the engine off while stopped and use the hydraulic technology to “launch” the car from a stop. Like any other hybrid, the results wouldn’t be as good on the open road.
I see where you’re coming from,
but the numbers you usually see for city/highway mpg are like 15/20, etc.
Doubling doesn’t make sense...