Turboroundabouts

Abstract

A "turboroundabout" is a variation of the conventional multilane roundabout in which spiral road markings and raised lane dividers force drivers to follow a specific path according to their intended destination. This geometry eliminates weaving and cut-in conflicts by guiding drivers continuously from entry to exit. Turboroundabouts were conceived with the main aim of improving safety, but their practical benefits are relatively unknown. Likewise, the few existing studies on turboroundabouts do not allow definitive conclusions to be drawn about the delay and emissions performance characteristics of turboroundabouts; further research is needed. This research focused on the use of appropriate modeling methodologies to understand the effects of turboroundabouts on capacity, safety, and emissions in comparison with the effects of conventional singlelane and double-lane roundabouts. The results indicate that turboroundabouts have capacity levels comparable to those of two-lane roundabouts but are less robust concerning the directional split of the entry traffic; turboroundabouts lead to fewer traffic conflicts, but the traffic conflicts that do occur are more severe. The results also show that the implementation of turboroundabouts provides no advantages for emissions when the main concerns are carbon dioxide and oxides of nitrogen.

Performance Assessment of Turbo-roundabouts in Corridors

“…The transformation of a conventional two-lane roundabout into a turbo-roundabout resulted in a reduction of the frequency of potential accidents between 40 and 50%, as there is a positive linear correlation between the potential number of accidents and the traffic volume. Also Vasconcelos et al (2014) found benefits in terms of safety. Using microsimulation techniques and SSAM software (Surrogate Safety Assessment Model), a comparative performance analyzes between single-lane roundabouts, multi-lane roundabouts and turbo-roundabouts was developed.…”

“…In recent studies carried out by Vasconcelos et al (2012Vasconcelos et al ( , 2014, the main differences affecting the capacity estimates, and based on the Hagring formula are shown and it was concluded: (i) the capacity of the major road entries of turbo-roundabouts are always lower than the conventional roundabouts because the opposite traffic flow is only concentrated in one lane of the circulatory carriageway; (ii) the relative performance of turbo-roundabouts decreases with increasing demand in the main direction, reaching capacity losses of 40%; (iii) in secondary entries, turbo-roundabouts ensure better performance, but only for specific demand scenarios, especially with very high proportion of right turns (above 60%). These results show the importance of the analysis, as the performance of the turbo-roundabout undeniably depends on the traffic volume and on the traffic distribution.…”

“…Although there is a general consensus about the improvements to road safety, the same is not true in terms of capacity, as there are authors who point to a general increase in capacity, while others contest these results. In turn, the studies about pollutant emissions are still extremely scarce (Vasconcelos et al, 2014) as there are no general conclusions about its true impact in terms of local and global pollutants. Therefore the development of further research is justified so that it can contribute for a better understanding of the real performance of turbo-roundabouts, based on different levels of demand and traffic distribution.…”

Geometric design of turbo roundabouts

“…Previous studies conducted on turbo roundabouts [8][9][10][11][12][13][14][15] were mainly based on evaluation of their performances (capacity, delays), and environmental, economic and safety benefits, in regard to single-lane, standard multilane, flower and target roundabouts. Turbo roundabout geometric design was considered in a number of other studies [1, 16÷19], which were generally focused on analysis of Dutch turbo roundabout geometry and presentation of new design approaches.…”

Improving the Sustainability of Transportation: Environmental and Functional Benefits of Right Turn By-Pass Lanes at Roundabouts

“…Figure 1). These additional lanes can also be installed at conventional roundabouts and at more recently designed roundabouts, such as turbo-roundabouts [5][6][7][8], C-roundabouts [9], target-roundabouts [10] and flower-roundabouts (the layout of the latter is just characterized by bypass lanes at each arm [11]). Right-turn bypasses increase conflict points between vehicles and between vehicles and pedestrians/cyclists [12][13][14][15] and, to a modest extent, the number of accidents [16].…”