Comparison of Procedures to Estimate Critical Headways at Roundabouts

Vasconcelos, Luís; Seco, Álvaro; Silva, Ana Bastos

doi:10.7307/ptt.v25i1.1246

Cited by 45 publications

(33 citation statements)

References 16 publications

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“…The results revealed important specificities of the methods with significant effects on the capacity estimates. The comparison of the estimates with values from several countries indicated significant differences among them and suggested the presence of relevant driving style differences; as a consequence, Vasconcelos et al [55] came to the conclusion that locally calibrated, country-specific, parameters should be preferred for capacity calculations.…”

Section: Portuguese Studiesmentioning

confidence: 97%

“…In another study Vasconcelos et al [55] estimated critical headways and follow-up times basing on observations at six Portuguese roundabouts; gap-acceptance data were collected at each entry, for the left-and right-lanes independently. The Authors applied several estimation methods: Siegloch [51], Raff [47], Wu [38], maximum likelihood [19] and logit method [54].…”

Section: Portuguese Studiesmentioning

confidence: 99%

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Gap-accepteance parameters for roundabouts: a systematic review

Giuffrè

Granà

Tumminello

2015

Eur. Transp. Res. Rev.

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Purpose The critical and follow-up headways are the two gap-acceptance parameters which explain the traffic interaction of a minor street vehicle when enters the roundabout, merging into or crossing one or more circulating (major) streams. Several studies and researches provide measurements of critical and follow-up headways from real data at roundabouts. The objective of our research is to synthesize the data from the series of selected studies to interpret variation across the studies. Methods In order to match the research goal, a systematic literature review on estimations of critical and follow-up headways at roundabouts was undertaken. Since several studies and researches developed worldwide were examined, we were able to note that the effect size varied from study to study. Thus the meta-analysis of effect sizes was performed as part of the literature review through the random-effects model. Results After discussing the assumptions of this model, the dispersion in effects across studies was assessed and the summary effect for each of the parameters under examination was computed. Calculations were made both for single-lane roundabouts and double-lane roundabouts, as well as for turbo roundabouts. Conclusions Compared to the results of individual studies, the single (quantitative) meta-analytic estimate provides an accurate and reliable synthesis on the specific issue here addressed, and gives, with greater power of the individual reviewed studies, a comprehensive measure for the parameters of interest.

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Section: Portuguese Studiesmentioning

confidence: 97%

Section: Portuguese Studiesmentioning

confidence: 99%

Gap-accepteance parameters for roundabouts: a systematic review

Giuffrè

Granà

Tumminello

2015

Eur. Transp. Res. Rev.

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“…Previous research from several countries has clearly shown that a properly designed roundabout can significantly improve traffic efficiency and road safety [6,7,8,9].…”

Section: Figure 1 -Ultra-large Roundabout In Livornomentioning

confidence: 99%

Upgrading Traffic Circles to Modern Roundabouts to Improve Safety and Efficiency – Case Studies from Italy

Pratelli

Sechi

Souleyrette

2018

PROMET

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This paper presents a procedure for analysing safety and operational improvements made possible by converting traffic circles to modern roundabouts. An Italian case study is presented for alternative layouts under various traffic demand scenarios. In the application of the procedure, the average waiting times and queue lengths at entries are computed with an analytical capacity model, using default values for gap parameters. Then, the roundabout is dynamically simulated. The simulation results in a revised set of gap parameters that are in turn used as inputs to a second trial of the capacity model, and in turn fed back into the simulation. The two steps are repeated until the parameters reach a pre-selected convergence criterion, so that gap parameter values for both the static capacity and dynamic microsimulation models are in equilibrium. Therefore, the applied procedure can conduct both static and dynamic roundabout design, usually applied separately. One can start with default values in guidelines and couple them with limited field data, improving both the expected results and cost-effectiveness of solutions. Next, safety is estimated using dynamic simulation software and a compatible conflict counting model to acquire surrogate measures of safety. Level-of-service and surrogate safety indicators for the existing and redesigned roundabouts are then compared. The procedure is first demonstrated on an old "ultra-large" roundabout. The procedure is tested on this roundabout using the Highway Capacity Manual 2016 (HCM2016), Aimsun TM , and Surrogate Safety Assessment Model (SSAM) software. A redesign is shown to be far superior in efficiency and safety. Finally, two cases are described where large first generation roundabouts were upgraded to modern standards. KEY WORDS traffic circles; modern multilane roundabout capacity models; multilane roundabouts design; operational efficiency analysis; traffic flow simulation;Pratelli A, Sechi P, Souleyrett RR. Upgrading Traffic Circles to Modern Roundabouts to Improve Safety and Efficiency -Case Studies from...

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“…Therefore, predicting the potential operating speed at a roundabout, during its design stage, is vital to ensure that the expected operating speed will meet the design expectations and the safety target for that roundabout. Furthermore, the capacity of a roundabout is highly correlated with critical time headways and follow-up times selected by drivers [5][6][7][8][9], which are related to the operating speed at the roundabout [2,[10][11][12][13][14]. Therefore, predicting the operating speed will also help in estimating the potential capacity of the roundabout being designed and ensure that the capacity meets the design requirements and the expected traffic volume.…”

Section: Introductionmentioning

confidence: 99%

Predicting Operating Speeds at Urban Multilane Roundabouts in Abu Dhabi, United Arab Emirates

Almoarawi

Dabbour

2018

Journal of Advanced Transportation

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There are more than 460 multilane roundabouts located in Abu Dhabi, the capital city of the United Arab Emirates, and its surrounding areas. Most of those roundabouts have three entry/circulatory/exit lanes with large radii, which resulted in the majority of drivers exceeding the speed limits for those roundabouts. Those excessive operating speeds, along with lack of drivers' awareness of the proper rules of driving at roundabouts, have resulted in increased collision frequencies at Abu Dhabi roundabouts. In this paper, operating speeds were measured at 12 roundabouts in Abu Dhabi and those collected speed observations were used to calibrate regression models to predict the 85th percentile operating speeds at roundabouts in Abu Dhabi. Predicting operating speed at a roundabout, during its design stage, is necessary to ensure that the expected operating speed and capacity will meet the design expectations. Three models were calibrated to predict the entry, circulating, and exit speeds, respectively. The calibrated models were validated with data not used in calibration and they were found to be stable and robust. The findings of this research study will help engineers when designing new roundabouts in Abu Dhabi or other cities with similar characteristics. This research study also provides a methodological framework for other researchers when conducting similar speed studies for roundabouts in other cities or metropolitan areas around the world.

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Comparison of Procedures to Estimate Critical Headways at Roundabouts

Abstract: The capacity analysis of roundabouts in Portugal is

Cited by 45 publications

References 16 publications

Gap-accepteance parameters for roundabouts: a systematic review

Gap-accepteance parameters for roundabouts: a systematic review

Upgrading Traffic Circles to Modern Roundabouts to Improve Safety and Efficiency – Case Studies from Italy

Predicting Operating Speeds at Urban Multilane Roundabouts in Abu Dhabi, United Arab Emirates

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