Safety Effects of Converting Intersections to Roundabouts

Jensen, Søren Underlien

doi:10.3141/2389-03

Cited by 39 publications

(14 citation statements)

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“…A metaanalysis of several studies indicates that the number of severe accidents is significantly lower at roundabouts (46% reduction for injury accidents) but property damage accidents increase (+10%) (19). A recent before-and-after study in Denmark reports decreases of 47% for injury and 16% for property-damage-only accidents (20).…”

Section: Ssam Approachmentioning

confidence: 97%

Validation of the Surrogate Safety Assessment Model for Assessment of Intersection Safety

Vasconcelos

Neto

Seco

et al. 2014

Transportation Research Record: Journal of the Transportation R

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The surrogate safety assessment model (SSAM) is a software application that reads trajectory files generated by microscopic simulation programs and calculates surrogate measures of safety. This approach eliminates the subjectivity associated with the conventional conflict analysis technique and allows assessment of the safety of a facility under a controlled environment before accidents occur. The specific goal of this research was to validate SSAM as a tool for accident prediction at urban intersections. Two methods were used for validation. The first method compared the simulated number of conflicts from the use of SSAM and the predicted number of injury accidents from analytic models in three reference intersection layouts (four-leg priority intersection, four-leg staggered intersection, and single-lane roundabout). The second method compared SSAM results with conflicts observed on site in four real intersections: two priority ones and two roundabouts. The results indicate that, despite some limitations related to the nature of current traffic microsimulation models, SSAM analysis is an extremely promising approach to assessing the safety of new facilities or innovative layouts.In urban areas, traffic accidents are usually concentrated at intersections. Traditional approaches to estimating the potential risk of traffic accidents at intersections, which are based on historical crash data, include before-and-after analyses and accident prediction models. Both approaches have important limitations related to the complexity of safety factors and the poor quality of data, thus (a) compared with other traffic events, accidents are quite exceptional in that they result from a series of unhappy improbable actions and situations; (b) accidents are rare events, so it is troublesome to base traffic safety analyses at individual sites on accidents alone; (c) not all accidents are reported, and the level of underreporting depends on the accident's severity and types of road users involved; and (d) information on the circumstances preceding an accident is seldom available (1). In addition, the fact that accidents must occur before one can determine the risk of locations is, from an ethical point of view, a dis advantage (2). Therefore, specific evaluation techniques are required to take into account changes in traffic regulations or in the geometrical design of infrastructure so as to estimate the true effects of safety improvements. Moreover, regression models may not be transferable because they implicitly reflect road users' behavior, the vehicle fleet, and driving rules, which vary from country to country and even from site to site.The traffic conflict technique is an approach that overcomes the lack of good, reliable accident records, relying instead on observations of conflicts. A "conflict" is defined as a situation in which two or more road users approach each other in time and space such that they risk colliding if their movements remain unchanged (3). The necessary evasive action is usually braking but may also b...

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Section: Ssam Approachmentioning

confidence: 97%

Validation of the Surrogate Safety Assessment Model for Assessment of Intersection Safety

Vasconcelos

Neto

Seco

et al. 2014

Transportation Research Record: Journal of the Transportation R

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“…There are several studies reporting an increase of service levels and traffic flow when converting traditional intersections into roundabouts (Kimber, 1980;Louah, 1984;Stuwe, 1992;Akcelik et al, 1996). Increasing safety levels have also been mentioned in studies comparing before and after conditions (Flannery and Datta, 1996;FHWA, 2000;Persaud et al, 2001;Jensen and ApS, 2013), and in historical analysis studies (Gross et al, 2013). Therefore, roundabouts are increasingly proposed as an alternative method of managing conflict points in intersections (NHCRP, 2010).…”

Section: Introductionmentioning

confidence: 94%

Driver Behavior Characterization in Roundabout Crossings

Silva

Santos

Vasconcelos

et al. 2014

Transportation Research Procedia

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Roundabouts are widely accepted for their safety, capacity and environmental advantages. Although it can be easily recognized that the driver behavior is mostly related with the roundabout geometry. This paper presents a detailed characterization of the driver behavior while crossing three consecutive double-lane roundabouts in an arterial road. Driver behavior was described in three main levels: i) speed profiles; ii) lateral acceleration profiles; iii) roundabout geometry. It is shown that roundabouts can substantially reduce speed in the negotiation zone. The entry speed and influence zone depends on the desired speed in the upstream sections and on the roundabout geometric characteristics.

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“…Roundabouts have the potential to reduce both the frequency and severity of crashes compared to traditional intersections (signalized or stop-controlled). Several studies carried out show the safety benefits of replacing signalized intersections by roundabouts (Sakshaug et al 2010;Gross et al 2013;Jensen 2013;Brilon 2016).…”

Section: Introduction and Objectivesmentioning

confidence: 99%

“…In contrast, the positive safety effects of converting intersections to roundabouts are not clear for bicycles. Some studies have been shown significant safety improvement (Schoon, Van Minnen 1994) while in other studies the effect of converting intersections to roundabouts on cyclists' safety was unclear or even negative (Sakshaug et al 2010;Jensen 2013).…”

Section: Introduction and Objectivesmentioning

confidence: 99%

Cycling at Intersections: A Multi-Objective Assessment for Traffic, Emissions and Safety

2019

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This paper evaluated in an integrated manner the traffic performance, pollutant emissions and road conflicts between bicycles and motor vehicles at a signalized intersection. Two alternative scenarios were examined: (1) bicycles increment and motor vehicles replacement within the cycle-fixed traffic signal; (2) replacing the existing traffic control by a conventional two-lane roundabout and evaluating the impacts of bicycles increment. For each scenario, bicycle demand was varied from 9 to 270 bicycles per hour (bph). Traffic flow and vehicle dynamic data were collected from a three-leg signalized intersection in Aveiro (Portugal). The microscopic traffic model (VISSIM) paired with an emission (Vehicle Specific Power – VSP) methodology and safety (Surrogate Safety Assessment Methodology – SSAM) model were used to assess intersection-specific operations. The fast Non-Dominated Sorting Genetic Algorithm (NSGA-II) was used to find the optimal bicycle demands. The results showed that two-lane roundabout outperformed the existing traffic control, namely in highest bicycle demand scenario (number of stops and travel time reduced in 78 and 14%, respectively; CO2, NOx, and HC decreased 9, 7, and 12%, respectively). It was also found that the number of conflicts was significantly reduced (–49%) with this latter layout even in maximum bicycle demand scenario (270 bph). However, roundabout layout lead to more severe conflicts and potential crashes. The analysis showed that bicycle demands of 75, 95 and 110 bph delivered good environmental and safety outcomes for the intersection.

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Safety Effects of Converting Intersections to Roundabouts

Cited by 39 publications

References 0 publications

Validation of the Surrogate Safety Assessment Model for Assessment of Intersection Safety

Validation of the Surrogate Safety Assessment Model for Assessment of Intersection Safety

Driver Behavior Characterization in Roundabout Crossings

Cycling at Intersections: A Multi-Objective Assessment for Traffic, Emissions and Safety

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