Assessing vehicle emissions in urban areas: how to take into account vehicle real operating conditions and uses


Type de document
Résumé / Abstract
Accurately measuring vehicle pollutant emissions requires to consider actual use, traffic and operating conditions. Privatly-owned vehicles driven for their normal purposes by their drivers have been equipped with data acquisition systems and followed up in operation. Performed trips and experienced speeds are reported. ,. Statistical analysis of speed profiles (speed curve as a function of time) showed their specific features according to traffic conditions and allowed the drawing up of test cycles (INRETS cycles) representative of the following different conditions: congested or normal urban traffic, on the road or motorway traffics. Representative cycles for traffic in urban tunnels (Tunnel cycles) were also defined. Pollutant emissions of 70 vehicles representative of the French fleet and tested using actual cycles performed at steady speeds have been measured. Main parameters of vehicle unit emissions are discussed. Test speed level (average speed) and vehicles (engine type, age, capacity, tuning stage) are important variation factors. Actual speed profile is an essential aspect: steady speed tests underestimate emissions by about 30%, and the specific traffic conditions in 'Tunnel' cycles generate emission values differing from those obtained on INRETS cycles at identical speed level. The evolution of emissions has then been contemplated, mainly conditioned by changes in mileage, road vehicle fleet and regulations on their pollutant emissions: CO, HC and PAH emission decrease; NOx, C02 and particles high increase.

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