Analysis of roundabout capacity under high demand flows

Al-Madani, H. M. N.; Saad, Muhammad Hafiz Md

doi:10.2495/ut090211

Cited by 7 publications

(9 citation statements)

References 6 publications

(6 reference statements)

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“…Collinearity might be a problem if the purpose is to estimate the contribution of individual predictors since it entangles the effects of the predictors, complicating the interpretation. However, the fi tted model still is accurate since the overall model prediction is satisfactory [39]. Variance infl ation factor (VIF) measures the extent of collinearity presence.…”

Section: Methodology and Study Approachmentioning

confidence: 99%

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Modeling and calibrating capacity of large roundabouts

Al-Madani¹,

Pratelli²

2014

Int. J. SDP

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Roundabout models, available in the literature widely, vary between one method and another. Majority of the\ud models are solely based on circulating fl ow to estimate capacity. The relationship between maximum entry\ud fl ow of large dual and triple lane roundabouts and their geometric and traffi c characteristics is investigated\ud here for saturated fl ow condition using multivariate analysis. The developed model, based on the data gathered\ud from 13 roundabouts in Bahrain, matched the fi eld data reasonably well. The signifi cant predictors, out of\ud 60 tested ones, included circulating and exiting fl ows, number of entry and circulating lanes, circulating and\ud entry widths, inscribed diameter and fl are length. Capacities predicted through various international models\ud varied considerably with both the developed model and the fi eld data. The international models were then\ud calibrated against the model, and consequently the fi eld data, so as to have signifi cant match with the two. The\ud procedure followed in developing the model and calibrating the international models consisted of eight stages.\ud It involved identifi cation of signifi cant correlation of individual predictor with capacity, multivariate regression\ud analysis, model smoothing, multi-collinearity test, redevelopment of the model after adjusting the variables\ud causing collinearity, comparison analysis with seven known international models and calibration of the international\ud model. While UK, aaSIDRA and French models required around 50% reduction to match the developed\ud model and actual data; US FHWA and Swiss models required 25% reduction and US HCM and German models\ud required just 8% adjustments. Such clear variations call for further research. The fi ndings assist the urban planners\ud as when to shift from one type of intersection control into another involving roundabout, and vice versa

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Section: Methodology and Study Approachmentioning

confidence: 99%

“…Variance infl ation factor (VIF) measures the extent of collinearity presence. The acceptable VIF values are thought to be in the range of 10 [39]. All the predictors with high VIF values are removed from the earlier model.…”

Section: Methodology and Study Approachmentioning

confidence: 99%

Modeling and calibrating capacity of large roundabouts

Al-Madani¹,

Pratelli²

2014

Int. J. SDP

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“…Two years ago Al-Madani and Saad [1] developed an exponential model for capacity estimate of roundabouts with triple circulating lanes. The model was derived in respect to the entry capacity values obtained from a selected set of international models applied to actual data observed on thirteen large roundabouts in Bahrain.…”

Section: Introductionmentioning

confidence: 99%

Testing for a large roundabouts capacity model: experimental comparisons between Italy and Bahrain

Pratelli¹,

Al-Madani²

2011

WIT Transactions on the Built Environment

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It is well-known that the maximum traffic flow that a roundabout entry is able to accommodate depends on the amount of flow circulating in the roundabout carriageway that conflicts with the entry flow exiting from it and strictly related to the geometric characteristics of the roundabout. International guidelines deal with various capacity models requiring different input data and often lead to different results for the same roundabout entry. Recently, an exponential model has been developed for capacity estimates of multi-lane roundabout entries under different conditions of circulating flow and geometrical factors. Such a model was validated by Al-Madani and Saad on data gathered from a sample of existing large roundabouts in Bahrain. Calculations made, applying the developed model, or BAHR model, showed a reasonable fitting to computational data obtained from different international models, as German, French SETRA, American HCM, and so on. In this paper, we have collected traffic data during peaks or congested periods and measured geometry parameters on twelve large roundabouts located in Tuscany, Italy. The main goal was with a view to testing if the BAHR model could be well suited or not to Italian context. The same previous methodology applied for the BAHR model was followed and found a new exponential entry capacity model, called TUSC. Statistical tests are performed and the paper ends with some comments about the obtained results.

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“…Only approaches with dual entry lanes are considered in this study. The range of the measured geometric and traffic data have been presented in earlier works [12,33]. The classified entry traffic flow counts for the selected roundabouts were collected during both morning and evening peaks for each approach.…”

Section: Data Gatheringmentioning

confidence: 99%

“…The models are very simplistic and incorporate only circulating flow for dual and triple lane roundabouts. A more extensive model is also available for Bahrain, since wide variations in the estimated capacities were observed when compared with other international models [33]. The model though fitted the actual data well, still showed wide variation with other international models.…”

Section: Introductionmentioning

confidence: 99%

Calibration of international capacity models for dual lane roundabouts during saturation flow condition

Al-Madani¹

2012

WIT Transactions on the Built Environment

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Varying differences in the prediction of roundabout capacities were observed between various international models and field data. This study attempts to calibrate 7 international models for forced flow conditions. These include UK, aaSIDRA, Swiss, US FHWA, HCM, French and German models. These are compared with field data collected from 12 large roundabouts in Bahrain. They are compared considering scattered plots, Root Mean Square Error (RMSE) and t-tests. Each model is calibrated by a trial multiplicative factor which is then adjusted in an iterative manner until best match with actual data is achieved. The calibration adjusts the Y-intercept and the slope of each model. The calibration factors, based on the initial results, showed high variations in the adjustment factors between one model and another. The calibrated models showed substantial improvements and were fairly comparable with actual data. The UK, aaSIDRA and French models, with over 40% reduction, required the greatest adjustments to suite the field data. The FHWA model required 35% reduction and the German model required 15% increase to reasonably fit the field data. The HCM method required no adjustments and the Swiss model required a reduction of 5%. The calibration factors were as follows in respective order: 0.5225, 0.515, 0.585, 0.65, 1.16, 1.0 and 0.95. While differences in capacity prediction between one international model and another confuse the practitioners; calibrated models assist them to have just predictions regarding roundabout capacities during forced flow conditions. The developed calibrations require further investigation to reduce the deviation between the calibrated models and the actual data.

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Analysis of roundabout capacity under high demand flows

Cited by 7 publications

References 6 publications

Modeling and calibrating capacity of large roundabouts

Modeling and calibrating capacity of large roundabouts

Testing for a large roundabouts capacity model: experimental comparisons between Italy and Bahrain

Calibration of international capacity models for dual lane roundabouts during saturation flow condition

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