The main losses are drag and, at low speeds, friction. A velomobile (enclosed bicycle or tricycle where you lie back) mostly solves the former. The effort of a

The main losses are drag and, at low speeds, friction. A velomobile (enclosed bicycle or tricycle where you lie back) mostly solves the former. The effort of a light walk moves you at about 30km/h on the flat (but slightly slower than walking on a steep uphill). Steel rails would make it slightly more efficient again.