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Eco-driving is an environmentally friendly driving manner which improves fuel economy. Since Eco-driving has an immediate and significant effect on improving vehicle's fuel economy, introduction of devices, that main functions are measuring vehicle speed and elapsed time on-board, making alerts when drivers deteriorate fuel economy, and recording driving patterns, is being promoted to support Eco-driving. However, fuel economy improvement rates by Eco-driving show uneven distribution because many factors such as the weather, road and traffic conditions, types of vehicles and drivers' individualities have influence on fuel economy. In this research, correlations between fuel economy improvement and drivers' individualities were examined on a proving ground. Then, in order to estimate the effect of fuel economy by Eco-driving in real traffic conditions, test drives using more than 1,000 trucks were carried out for 5 months with compared to the data of no Eco-driving.

Hybrid trucks have now started to penetrate the Japanese market. To investigate their advantages for fuel economy and exhaust emissions, a real time on-board measurement system for fuel economy and NOx emissions was mounted in a medium duty hybrid truck with a capacitor system. Running tests were carried out with various payloads on roads. The results demonstrated the advantages of the hybrid truck in real traffic conditions. Fuel economy was improved on urban and suburban roads, as compared to a base diesel vehicle. The hybrid truck showed less NOx emissions during acceleration at starting, whereas, acceleration of diesel vehicles may cause intensive localized NOx pollution of roadsides, in places like intersections.

An on-board measurement system that simultaneously measures road traffic, vehicle running conditions and exhaust emissions was installed in a diesel freight vehicle with two tons payload. Actual NOx mass emissions were compared with that measured in a typical test mode for urban cities on a chassis dynamometer. The frequency of vehicle accelerations in actual urban cities was found to exceed that of a typical test mode for urban cities on a chassis dynamometer, which resulted in increased NOx from actual running conditions compared with the typical test mode for urban cities. The dynamics of NOx emissions at an actual roadside was also analyzed. It was observed that NOx emission based on distance with an actual city route test was about two times higher than that of a free way route and a typical test mode for urban cities. The reason for high NOx with the city route was explained by the higher frequency of lower gears at which higher NOx is emitted.

Hybrid trucks are disseminated on the market in Japan. To bring out advantages of fuel economy and low emission, on-board measuring system for fuel consumption and NOx emissions was mounted in a light duty truck with a parallel hybrid system. Tests were carried out with various payloads on roads. As the results, advantages of the tested hybrid truck were shown from the actual data regarding the fuel economy and NOx emissions, considering regeneration energy by the hybrid system. Improvement of the fuel economy and NOx emissions was clearly observed in the running condition such as urban and suburban roads. From the analysis of regeneration energy during vehicle deceleration, it turned out that a longer slowdown time and a higher speed at which deceleration begins result in larger amount of energy regeneration, which means the improvement of fuel economy. For the improvement of roadside pollutions, the reduction of NOx emissions in running using the second gear position is desired.