In this master’s thesis a fleet of 18 passenger and light commercial vehicles with an imbedded vehicle tracking system via GPS has been assembled. The devices collect data concerning time, location and speed of vehicles, while in late models they collect additional data such as engine speed, gear ratio and current fuel consumption via CAN bus. As the path, speed and acceleration give the basic description of a motion of a vehicle, these parameters can be used as the basis of defining the behaviour of a certain driver in traffic. Based on a large number of collected data, a way of testing driving style was designed for evaluation purposes. Depending on the value of parameters such as travelled distance, speed and acceleration, an RPA (Relative Positive Acceleration) rating has been given. For driving reviews or definition of aggressive or non-aggressive driving, one of the most important parameters is acceleration. The RPA’s value has shown its consistency at all driving speeds, and the acceleration had the biggest impact on it. In the second part of the thesis, the influence of the electrolysis devices on the emission of harmful substances from the vehicle was investigated. There are more and more devices showing up on the market claiming that their actions can affect the passage of vehicles on the emission test at periodical technical inspection. The observed unit of the devices most often works on the electrolysis principle whereby water molecules are separated into hydrogen and oxygen molecules, and then the gases are sucked into the engine together with the ambient air. The emission test was conducted in total of four times, from which two times were conducted before the “cleaning” procedure and two times after. The first measurement was carried out to establish the standard vehicle emission limit. The vehicle cleaning procedure was undertaken after second measurement which was followed up by third measurement. Last measurement was performed as a control measurement to determine the effects of the device. In the driving test, it was possible to determine the difference in vehicle utilization during the before “cleaning” period and after the „cleaning“ of the vehicle.