Speed limits and their impact on emissions production and fuel consumption

M. Kotek, P. Jindra* and J. Mařík

Czech University of Life Science Prague, Faculty of Engineering, Department of Vehicles and Ground Transport, Kamýcká 129, CZ16521 Prague, Czech republic
*Correspondence: jindrap@tf.czu.cz

Abstract:

The article deals with emissions and fuel consumption of road vehicles in real traffic conditions. The aim of this study was to prove or disprove correctness of the decision of Prague city government to change the speed limits from 70 km h-1 to 50 km h-1 on the parts of one main road leading to/from Prague. For measurements in real traffic conditions was used 2 typical Czech cars Skoda with manual transmission (Fabia 1.2 MPI with petrol engine and Octavia 2.0 TDI with diesel engine). Measurements were performed on both of directions on defined road segment.

At speed 50 km h-1 the measurement was repeated 5 times at 3rd and 5 times on 4th gear. Similarly at speed 70 km h-1 the measurement was repeated 5 times at the 4th and 5th gear. The aim was to operate the vehicle in the normal engine loads.

The results demonstrate the fundamental assumption that at the higher allowed vehicle speed the engine is more loaded and therefore produces a higher amount of emissions, but according to a higher vehicle speed the emissions are produced on the defined segment for the shorter time. A similar trend is evident even in fuel consumption. The results also indicate the depending on the power reserve of specific vehicle. When the vehicle is more powerful, higher permitted speed is preferable.

Key words:

emission, fuel consumption, on-road measurement, speed limit, vehicle