BENEFITS OF RAISED LANE DIVIDERS ON TURBO-ROUNDABOUTS IN TERMS OF TRAFFIC SAFETY AND CAPACITY

References: 17th International Multidisciplinary Scientific GeoConference SGEM 2017, www.sgem.org, SGEM2017 Conference Proceedings, ISBN 978-619-7408-13-3 / ISSN 1314-2704, 29 June - 5 July, 2017, Vol. 17, Issue 62, 487-494 pp, DOI: 10.5593/sgem2017/62/S27.062

ABSTRACT

In the last years, turbo-roundabouts replace conventional multi-lane roundabouts with aim to ensure a higher level of traffic safety and capacity. The most important feature of turbo-roundabouts is a spiral course of the circulatory carriageway allowing drivers easily pass through the roundabout from the entry – circulatory carriageway – to the exit without a need to change traffic lanes. Despite of an original proposal assuming the physical separation of spiral lanes, in many countries, the lanes are “separated” with a horizontal road marking only. However, experiences which were observed at turboroundabouts have shown that about 40% of drivers act in illegal behaviour. The ignorance of traffic rules primary leads to an increasing a crash risk and secondary it leads to an inefficient use of both lanes at the entries and on the circulatory carriageway, such as it is on standard two-lane roundabouts. So, the physical separation of traffic lanes has significant importance to ensure a higher level of road safety and subsequently even an efficient use of both lanes at the main “turbo” entries. The effective use of both left (inner) and right (outer) entry lane has a positive impact on the capacity of two-lane entries. In the article, this effect was calculated using a theoretical capacity model. The results show, for example, an increase in the potential two-lane entry capacity about 19% by increasing the left lane use from 40% to 50%.

Keywords: turbo-roundabout, raised lane dividers, capacity, traffic safety