The aim of the study is to verify the thesis about the influence of the vehicle speed on the exhaust emissions. The influence of the speed on the fuel consumption is quite easily measurable and generally possible to identify, while determining the emissions of harmful substances requires specialized research equipment. The analysis is important from the point of view of the vehicle operation. The paper presents the results of the road tests of a car fitted with a diesel engine. It contains the results of measurements of the concentration of the exhaust components. In the measurements, PEMS portable equipment was used. The study was conducted under actual traffic conditions (motorway driving) on a selected portion of the A2 motorway, located near Poznan.