The impacts of a green-driving application on fuel consumption, speeding and passenger comfort were assessed on a frequently operated bus route in the Helsinki metropolitan area. The main results of the study show that use of a green-driving application in buses significantly reduces fuel consumption and speeding and increases passenger comfort. Novel users of the system drove more economically than those who had used the system longer, but the impact was smaller than found in previous studies. In addition to savings on fuel, the application encouraged driving within the speed limit. A transfer effect on journeys without the system was found for long-term users but not for novel users. Furthermore, passengers of drivers who used the green-driving application gave better grades for decelerations and the driver’s service attitude in peak traffic. The authors main conclusion is that use of a green-driving application is beneficial even after years of use for reducing both fuel consumption and speeding. The authors recommended that drivers be regularly encouraged to use the system and that green driving be included in driver training.