Optimizing Geometric Design of Standard Turboroundabouts
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pISSN 1226-7988, eISSN 1976-3808 www.springer.com/12205
DOI 10.1007/s12205-020-1689-3
Transportation Engineering
Optimizing Geometric Design of Standard Turboroundabouts Tamara Džambas
a
, Vesna Dragčević
a
, and Željko Korlaeta
a
Dept. of Transportation, Faculty of Civil Engineering, University of Zagreb, Zagreb 10000, Croatia
ARTICLE HISTORY
ABSTRACT
Received 18 September 2019 Revised 13 January 2020 Accepted 28 May 2020 Published Online 17 August 2020
Previous studies have shown that existing turboroundabout design procedures, in which swept path analyses are conducted at the end of design process, contain certain disadvantages and understatements which can lead to oversized or undersized turboroundabout solutions i.e. low intersection capacity, poor traffic safety, low driving comfort and high construction costs. Within the scope of this study elements of standard turboroundabouts were designed in accordance with the design vehicle movement trajectories obtained by the swept path analyses. Reliability of the software used in these analyses was verified by the real drives at the test site. Geometric design of standard turboroundabouts was conducted with variation of following influential parameters: design vehicle; circulatory roadway radii; approach leg offset and angle value. Design approach applied in this research resulted in optimal intersection design regarding the occupation of surrounding area and the design vehicle swept path requirements. Circulatory roadway radii and approach leg offset and angle limit values applicable on this intersection type are determined, taking into account the real traffic situation. Additional practical contribution of this research lies in the ability of application of research results in revision of existing guidelines for the design of turboroundabouts, as well as in development of new guidelines in countries which still do not have their own regulations on the design of this rather new multilane roundabout type.
KEYWORDS Standard turboroundabouts Geometric design Swept path analysis Design vehicles Vehicle movement geometry Optimization
1. Introduction Turboroundabouts are specially designed multilane roundabouts with spiral circulatory roadway and physically separated traffic lanes (Fortuijn, 2009; Fortuijn, 2012). This roundabout layout was developed by a Dutch researcher dr.ir. L.G.H. Fortuijn in the late nineties of the last century with the aim of increasing the traffic safety and capacity at classic multilane roundabouts (Tollazzi and Renčelj, 2014; Tollazzi et al., 2015; Pitlova and Kocianova, 2017; Alsaleh and Shbeeb, 2018; Guerrieri et al., 2018). Previous studies conducted on turboroundabouts were mainly based on evaluation of their performances (capacity, delays), and environmental, economic and safety benefits in regard to singlelane, classic multilane, flower and target roundabouts (Mauro and Branco, 2010; Tollazzi et al., 2011; Giuffrè et al., 2012; Tollazzi et al., 2013; Vasconcelos et al., 2014; Bastos Silva et al., 2015; Guerrieri et al., 2
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