The big thing about any of these systems is to be able to recover/store energy from braking, that's what produces the high MPG figures IMHO.
With hydraulic fluids, which are incompressible, a gas must be compressed within the accumulator, maybe an air powered vehicle is next in line, as in compressor plus air motors. Wonder what size accumulator it would take to brake, going down a mountain, stop and go in traffic is one thing.
What happens when a highly charged accumulator is punctured?
Other systems include flywheels, which are engaged during braking and store energy by spinning at a high speed, a very old technique...
Electric batteries are nice since they can be charged by a number of methods, including the sun, still very heavy, though.
Hybra = hydraulic braking? ......"bra"...they could have done better picking a different name..
Just thinking out loud here.
