There is no separate braking system. It is simply a mode the car switches into in which the electric motor becomes a generator transfering the kinetic energy of the car into potential energy (charging the battery) thereby slowing the car. Press the brake a little more and the actual disc/drum brakes kick in as well.

I'm all for a spirited discussion about the merits of these hybrids, but there seems to be alot of disinformation out there about these cars. My wife had the original model and now drives the second gen prius. Zero problems, excellent mileage and a much safer/roomier vehicle now. Me, I prefer the diesels.

Kevin
1979 240D manual
1984 190D manual