Many city in Indonesia still allow becak to operate. Traditional becak have no engine, it cheaps, slow, and become king of transportation because another street user have to aware of becak since it can entering street suddenly & silently from crowd without warning.These machines would otherwise glide silently past but for a piece of gut stretched tight beneath their carriage. It produces a distinctive pretty modulated buzzing sound to alert pedestrians of the Becak's presence. There is also usually an old bolt tied to the handle bar with an elastic band. The driver uses this device to demand a clear passage in crowded conditions. The resulting metallic 'clackety, clack clack' sound resonates around the frame of the Becak. The Becaks of Solo use large gongs to forge their way in traffic.