Empirical Assessment of Turbo-Roundabout Operations on Traffic and Emissions

In the past decade there has been a significant increase in the number of turbo-roundabouts constructed in several European countries. This paper investigates the impact of turbo- roundabouts located in urban areas on pollutant emissions generated from vehicles through an empirical assessment. The research also compares the emissions of vehicles moving through a turbo-roundabout and a conventional multi-lane roundabout. Based on field measurements taken at turbo-roundabouts and multi-lane roundabouts located in Grado (Spain) and Aveiro (Portugal) three representative speed profiles for each speed trajectory type were identified: no stop (I), stop once (II) and multiple stops (III). This study also develops discrete models for turbo-roundabouts and multi-lane roundabouts in which the relative occurrence of those speed profiles is expressed as a function of the entry and the conflicting traffic flows. The Vehicle Specific Power (VSP) methodology is employed to estimate second-by-second pollutant emissions. This research testes the hypotheses that emissions are impacted by the differences in: 1) the characteristics of speed profiles in each movement; 2) the volumes of entry and conflicting flows; 3) the overall saturation level; and 4) the transportation facility considered (turbo-roundabout /multi-lane roundabout). The results show that vehicles emit more pollutants at turbo-roundabouts compared with multi-lane roundabouts regardless of the traffic demands at the entry and the circulating areas. These findings suggest that there are no advantages on implementing turbo-roundabouts from an environmental point of view even the capacity of the intersection is rather below to the maximum.