This paper provides an insight into the engineering techniques used during the preliminary design, optimisation and final construction of a prototype regenerative braking system which has been retrofitted into a Leyland Panther bus. The system studied utilises a single hydrostatic pump/motor unit which regulates energy flow into and out of hydraulic accumulators.The accumulators, hydrostatic pump/motor and regenerative system have been optimally configured and designed using a probabilistic and statistical approach in conjunction with digital computer simulations. Computer aided design has been used throughout the construction of the prototype system with full advantage being taken of the three dimensional modelling capabilities. The digital control system developed provides tremendous flexibility enabling various near-optimal control algorithms to be utilised for operation over various bus routes. The bus is currently being evaluated whilst in service carrying passengers around the environ's of Brisbane City.