Assessment of vehicle emissions at roundabouts: a comparative study of PEMS data and microscale emission model

Energy efficiency has a central role to play in achieving decarbonisation targets in the transport system by changing the demand for mobility (eg. by influencing on peoples behaviors) and improving the performance of the fleet. In recent years there has been an increase of use of private transport, partly due to the recent pandemic and the reduced choice of public transport. People's travel habits have changed in frequency and motivation due to the reduced number of seats on public transport, due to social distancing but also due to online education and teleworking. This increase of use private cars has led to an increase in environmental emissions as a result of the high proportion of vehicles with combustion engines in urban areas. The highest concentrations have been recorded at road intersections and in particular at roundabout configurations where there is a higher number of stop-and-go's overall. The increasing importance of air pollution from vehicle traffic has suggested that environmental considerations should be added to these aspects as a criterion for intersection design. Several studies in the literature analyze the environmental emissions generated by vehicle traffic using different methods such as on-site recording, mathematical modeling of dispersion phenomena, micro-simulation of vehicle traffic, use of appropriately equipped vehicles with sensors. This paper presents a comparison between the results obtained from the Portable Emission Measurement System (PEMS) and the results obtained from the VERSIT+ emission model. Specifically, using a Portable Emission Measurement Systems (PEMS) installed on a series of test cars, instantaneous CO2 and NOX emissions were measured on repeated trips along two-lane roundabout intersections. The study was carried out by examining a selected two-lane roundabout in the city of Rzeszow (Poland) using 9 different vehicles fueled by petrol, diesel, and LPG. The results show that the investigated VERSIT+ emission model used led to an inaccuracies in the calculation of CO2 and NOx emissions. Furthermore, current micro-scale emission models may not estimate emissions of harmful exhaust components with sufficient accuracy due to the specificities of roundabout driving. Therefore, there is a strong demand for the development of new emission models, adapted to the driving behavior of drivers appropriate for different infrastructure objects such as roundabouts