In the large cities of Asian countries, the traffic flow at many intersections is controlled by traffic signals. Most of the vehicles there are obliged to stop or to decrease their mean speed. For the purpose of reducing the fuel consumption of vehicles, the authors paid their attention to the method of passing through a series of traffic signals and carried out the experiments for several traveling modes of the vehicles.As a result, we proposed to the drivers that they drove according to the controlled-traveling-mode which consisted of controlling the speed, the acceleration and the deceleration of the vehicle according to the time interval of each traffic signal. When a driver was forced to run in the controlled-traveling-mode instead of the ordinary- traveling-mode, the fuel consumption of the vehicle improved about 20 percent although the traveling time was the same. The improvement was 10 percent for a group of traveling vehicles. The improvement for the actual traveling on the road could be also attained successfully, when the driver was warned beforehand and given information of upcoming signals by the subsidiary-device.