Ive long thought Dernys were cool. they are as i read, a particular design made for pacing racers around the track on bike races.
Its somewhat like a 49cc moped but geared pretty high so the Derney driver slowly increased his pace , with the pedals
pulling the racer behind him in his wind break, then the cyclists ride the last couple laps around the track with out the motor pace..
A featured part of the wintertime indoor 6 day racing events.
http://upload.wikimedia.org/wikipedia/en/b/bc/Derny.jpg