M.Sc Student | Hamoudeh Wafa |
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Subject | Evaluation of Models to Estimate Capacity of Two-Lane Roundabouts |

Department | Department of Civil and Environmental Engineering |

Supervisor | Professor Abishai Polus |

Full Thesis text - in Hebrew |

This study presents and compares methodologies that evaluate models to estimate entry capacity of two-lane roundabouts.

Entry capacity is a main indicator used by most countries to assess roundabout performance. Entry capacity depends mainly on circulating flow. Many countries have developed their capacity models based on two methodologies which assess the entry/circulating relationship: regression analysis and gap acceptance theory.

This study presents entry capacity, delay and queue length comparisons for three roundabout categories: one-lane roundabout, two-lane roundabout with one-lane entry and two-lane roundabout (in circular roadway and in entry).

In order to estimate the entry capacity for two-lane roundabouts in Israel, data was collected done in two roundabouts. These roundabouts consist of two-lane circulating roadway and four-legs with two-lane entry at each approach. Every roundabout has different environmental conditions which affect on its safety, traffic operations and performance.

Based on the data that was collected, a negative exponential regression function was calibrated to estimate the entry capacity of two-lane roundabout which shows a decrease in entry capacity when the circulating traffic volume increases.

Based on both the rejected and accepted gaps observed in the entry lanes and circulating roadway, the critical gap and the follow-up time were estimated in entry lanes of the two tested roundabouts in Affula. In addition, the distribution of the traffic volume in each entry lane has been estimated to determine the dominate stream and the distribution of traffic volume in the circulating lanes in order to evaluate its effects on entry capacity of two-lane roundabouts.

To estimate the distribution of the follow-up observations in the entry lanes, a linear regression were fitted in order to determine whether the follow-up time changes as a function of the circulating flow.

It was concluded that the environmental conditions of the roundabout and its location (rural vs. urban area), the distribution of traffic flow in the two circulating lanes has an impact on entry capacity of two-lane roundabouts.

In addition, limited sight distance and disturbances caused by buildings located near the entry, pedestrians crossing the entry with priority over vehicles, misapprehension of the geometric design of the two-lane roundabout have a negative effect on the entry capacity of two-lane roundabout.