A turbo roundabout is a new type of canalized multilane intersection in which the physical separation between lanes helps to\ud prevent side collisions when crossing the roundabout. This paper presents an estimation of capacity, delays and level of service\ud of basic turbo roundabouts in undersaturation conditions, considering both vehicle flow and pedestrian traffic. The traffic\ud performance model was developed by evaluating the capacity for each entry lane. Owing to the geometric features of the\ud intersection, the total entry capacity is obtained by considering different values of the pedestrian impedance factor and degree\ud of saturation at both the right-turn and left-turn lanes

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Abstract:The functional performances of conventional roundabouts (single-lane and multi-lane) and innovative roundabouts (spiral, flower, C and turbo) can be improved through right-turn bypass lanes controlled by stop, yield or free-flow signs. The article presents evaluations of the emissions of air pollutants (carbon dioxide, nitrogen oxides, particle pollution (PM10 and PM2.5)), fuel consumption and construction, management, energetic and environmental costs in roundabouts without or with bypass lanes (controlled by stop, yield or free-flow). The suggested methodology has a general character and can be applied as a multi-parametric criterion for choosing road intersections, although, in the present paper, it has been employed only for a case study. For the aims of this research, we employed recent closed-form formulations to determine roundabout performances; moreover, we used the COPERT IV ® software to estimate air emissions in nine different types of vehicles. Numerous traffic simulations were carried out. The variation in the maximum hourly traffic Qmax and annual traffic QTOT provided the appropriate domains of the examined geometric layouts, both in functional and environmental terms and with regard to generalized costs, estimated for a 10-year period. It resulted that the introduction of right-turn bypasses in all arms of conventional roundabouts with a one ring lane and one lane at the entries (single-lane roundabouts) is the most cost-effective when the flows entering the roundabout are higher than Qmax = 2000 veh/h. Moreover, free-flow bypass lanes always OPEN ACCESSSustainability 2015, 7 5839 provide greater capacity and lower delays than stop-or yield-signaled bypasses. However, with extremely high Qmax values, stop-controlled bypasses guarantee lower fuel consumption, while those with a yield sign lower total costs.

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