JAKARTA -- There is a new sight in central Jakarta, something you never saw only a year ago: motorcycle drivers wearing bright green helmets and uniforms, cruising by with passengers on their back seat. They are drivers for Go-Jek, a service that hails the city's "Ojek" motorcycle taxis via a smartphone app.

The change is proving popular with commuters. In Jakarta, they are springing up on the street like grasshoppers. Go-Jek's app, launched in Jakarta in January, quickly registered more than 10,000 drivers and 650,000 downloads. The service has expanded to three more cities.