Comparing Performances of Turbo-roundabouts and Double-lane Roundabouts

Abstract

Starting from assumptions regarding the arrival process of circulating streams and according to models based on the gap-acceptance theory, the paper is aimed at comparing operational performances between basic turbo-roundabouts and double-lane roundabouts. The paper proposes applications of the Hagring model for entry capacity estimations at double-lane roundabouts and turbo-roundabouts, these latter, in particular, featured by movements with only one or two conflicting traffic streams. This model allows to use, in fact, a bunched exponential distribution to quantify the distribution of major vehicle headways; it also considers specific values different by each lane for behavioural parameters, minimum headway and conflicting traffic flow on circulating lanes.The results obtained for the two cases examined, although influenced by the underlying assumptions, especially with regard to user behaviour at turbo-roundabouts, can give information about the convenience in choosing, at a design level, a basic turbo-roundabout rather than a double-lane roundabout. The comparison developed in this paper, indeed, can be helpful in selecting the type of roundabout and in particular in evaluating performance benefits that are obtainable from the conversion of an existing double-lane roundabout to a turbo-roundabout with similar footprint of space.Keywords: turbo-roundabout, traditional roundabout, operating performaces Introducation Introducing the ProblemTurbo-roundabouts represent a new type of circular intersection which were designed to improve safety performances at modern roundabouts, already widely spread in the world, without compromising their efficiency. The turbo-roundabout is a specific kind of spiralling roundabout developed in The Netherlands by Fortuijn in the late 1990's. Fortuijn developed turbo-roundabouts in an attempt to deal with the drawbacks of double-lane roundabouts: while double-lane roundabouts have a higher capacity than single-lane roundabouts, they have the disadvantage of a higher driving speed through the roundabout and lane changing on the ring, hence raising the crash risk. Turbo-roundabouts were, indeed, introduced to deal with the entering and exiting conflicts occurring at double-lane roundabouts; these conflicts are eliminated at turbo-roundabouts by directing drivers to the correct lanes before entering the intersection and introducing spiral lines that guide them to the correct exit. On design principles and geometric elements of a turbo roundabout, as well as different variants of the turbo-roundabout progressively introduced in The Netherlands, can be seen e.g. Fortuijn (2009a). Other European experiences with turbo-roundabouts are referred by Brilon (2008) and Tollazzi et al. (2001).An exhaustive evaluation of safety performances at turbo-roundabouts is not yet available because turbo-roundabout installations are still recent. It follows that the design choice between a standard double-lane roundabout or a basic turbo-roundabout can be carried out through convenience evaluatio...

Gap-accepteance parameters for roundabouts: a systematic review

“…According to [8], entry capacity calculations at steady-state conditions can be performed through a variety of capacity formulas incorporating some information on the roundabout configuration, represented by the number of circle lanes and entry lanes [9,10], or other formulas incorporating some aspects of the roundabout geometry in somewhat detailed way [11], as well as formulas incorporating, together with geometric aspects, the users' behavior through the critical and follow-up headways (see eg [12][13][14]). Relevant concepts on capacity models at roundabouts can be found in [2,[15][16][17]. When critical headway and follow-up headway are involved, capacity estimations are being performed by analytical gap-acceptance models [8].…”

Flower Roundabouts And Double-Lane Roundabouts: A Comparative Performance Analysis

“…Although other studies have assumed the degree of saturation as comparison criterion for evaluating operational benefi ts of the innovative roundabouts over the modern roundabouts (see e.g. Mauro, Branco [26]; Giuffrè, Granà, S. Marino [27]), the control delay was used here as comparison criterion due to its relationship with the level of service. This paper is organized as follows: the proposed method to assess and compare the two roundabouts in Figure 1 in terms of operating performances is described in section 2, whereas the outcomes of the performance evaluations between fl ower roundabouts and double-lane roundabouts under different demand are summarized in section 3.…”

Airworthiness Support Measures Analogy to the Prospective Roundabouts Alternatives: Theoretical Aspects

“…Rational economic activity is the foundation providing the development in all areas and spheres of life [2]. Therefore, theoretical researches with the help of the plausibly developed hypothetical mathematical models are of a great importance [2]; moreover, the usefulness of such models application for the alternative roundabouts effectiveness evaluations is beyond any doubts and it can be traced with the most upto-date publications [3][4][5][6][7][8][9][10][11][12][13][14][15]. The brief literature survey of the presented paper just is highlighting the principal possibilities of the proposed methods implementations in those areas of science that relate with the multiattribute assessment of road design solutions [3], geometric design of turbo roundabouts [4], or the journal paper [5] dedicated to the turbo roundabouts, design principles, and safety performance, as well as alternativeness [6] and transportation infrastructure [7] aspects.…”

“…It is also necessary to underline the importance of the developed here approach for other transportation facilities, like railway [8]; however the methods are aimed at modeling alternative roundabouts effectiveness and in its sense continue the researches of the assessment, analysis, and simulation discussed in references [9][10][11][12][13][14][15]. Some of those publications emphasize the evaluation of the environmental and functional benefits of "innovative" roundabouts situational 2 Journal of Advanced Transportation features, like [11] or the study of the vehicle speed [14] for the design of the roundabouts.…”