While engine test procedures are mainly applied to verify and ensure compliance to the various emission standards, vehicle test procedures were developed to simulate the vehicle in actual service (including engine, drive train and chassis). These drive cycles are usually performed on a chassis dynamometer, but can also be performed on test track. The results are expressed in grams of pollutant per unit of distance (g/km). Examples of vehicle test cycles, which are mainly focussed at city buses, are the time-based Central Business District Cycle (CBDC) and the Dutch Urban Bus Driving Cycle (DUBDC) and the distance-based Belgian City Cycle of the public Transport Company “De Lijn”.
In the frame of the IEA-AMF project “Real Impact of New Technologies for Heavy Duty Vehicles”, three state-of-the-art city bus technologies were evaluated for fuel consumption and emissions both in real city traffic and in the mentioned vehicle test cycles. The three buses were a diesel bus, a natural gas bus with stoichiometric fuel control and three-way catalyst, and a natural gas bus with lean burn fuel control. The purpose of the project was to look for clear relations between various test cycles in the IEA-AMF countries and the correspondence of these cycles with real traffic.
The results show that the relation between real-city traffic and simulated city cycles differs from technology to technology. The acceleration capabilities of the bus are found to be very important, and the acceleration requirements of the simulated city cycle should match the actual capabilities of the bus.