## 2 Literature Background  
A historically significant achievement towards tracking pollutant emissions and fuel consumption in conditions corresponding to the actual use of motor vehicles was the introduction of driving tests performed on a chassis dynamometer [6; 12]. This type of tests allowed for considering dynamic driving conditions in contrast to the classic methods of testing combustion engines in static states [13]. The developers of driving tests strived to replicate realistic driving conditions in the laboratory as accurately as possible since the exhaust gas analyzers' technical constraints prevented accurate on-board measurements at that time [6]. The introduction of increasingly stringent exhaust emission standardscontributed to the further development of vehicle testing methods [5]. New legislation established limits for harmful substances in exhaust gases, the driving tests used so far were modified and new driving tests appeared, simulating with greater accuracy the driving conditions of cars for different road traffic models [14]. In the second decade of the 21 st century, efforts to incorporate vehicle testing in actual road conditions into legislation have accelerated [14]. This was largely due to the availability of advanced equipment that allowed for measurements of pollutant concentrations in exhaust gases with an accuracy comparable to that of equipment in stationary laboratories. However, the direct impulse to implementation of the above regulations was the results of studies conducted using portable emission measurement systems (PEMSs) [6]. They showed that the previous testing methods based on the chassis dynamometer do not fully reflect the real conditions on roads, being associated with lower emissions of some pollutants, especially nitrogen oxides [6; 15]. In 2015, an incident occurred involving one of the leading car manufacturers related to the optimization of the control of some engine models so that they exhibit reduced pollutant emissions in type-approval tests [16]. The above factors strengthened the actions towards the adoption in 2016 in the European Union of the first package of Real Driving Emission regulations, which specified procedures, requirements for equipment and criteria for the assessment of measurement results (Regulation EU 2016/427) [7]. Ever since the legal regulations on testing motor vehicles in RDE procedures were implemented, there has been a significant rise in the number of publications related to this topic. As the current literature is very rich, only some selected examples are discussed below. The first group of papers contain the results of vehicle tests performed according to RDE regulations, potentially examining the impact of some factors, i.e., driving conditions, various technical advances in vehicles, etc., on the results. For example, [PERSON] et al. [17] provided test results for two popular passenger cars with spark-ignition and compression-ignition engines in RDE tests. The factors under examination in that case were environmental conditions (winter and summer), road slope, altitude and driving style (mild and aggressive). The impact of the above factors was assessed, mainly based on the emission trends for carbon dioxide (CO\({}_{2}\)), nitrogen oxides (NO\({}_{\text{x}}\)) and particulate number (PN). Similarly, [PERSON] et al. [18] investigated the influence of technological aspects of vehicles on cold-start emissions in real driving conditions. Eleven vehicles with various variants of fuel injection, powertrain and aftertreatment systems were selected for testing. Measurements in real street traffic, at different temperatures, were conducted using PEMS. Some research works focus on comparing the results of real world on-road tests and regulatory driving tests performed on a chassis dynamometer. [PERSON] et al.