Abstract
With the growing number of vehicles utilizing roads in the city of Doha, Qatar, most intersections, particularly multilane roundabouts, have been facing traffic congestion dilemma, where traffic demand exceeds capacity. A new design for multilane roundabouts, known as a rotor turbo roundabout, was considered as an alternative to an existing highly congested multilane roundabout. The new design features spiral roadway markings and raised lane dividers which prevent maneuvering within the roundabout and eliminate cutting-offs and weavings. This design has achieved high capacity and low delay in many European countries. In this study, a traffic simulation program, VISSIM, is used to model the complex traffic operation of both the existing and proposed multilane roundabouts and to replicate the high traffic conditions and aggressive driving behavior prevalent among the Middle East countries. Three different rotor designs were examined in an attempt to have a valid comparison between the two types of roundabouts and to adhere to the standard design of the rotor roundabout without violating its essential features. The proposed designs performed slightly better on the minor approaches and managed to deliver an overall improved LOS compared to the conventional design. Major approaches, however, exhibited an increase in vehicle delay and queue lengths. The results showed that the capacity of the conventional three-lane roundabout was always superior to the capacity of the rotor roundabouts. It was concluded that rotor roundabouts may not be suitable for intersections with high demand volumes exceeding 4500 vehicles per hour, and whenever the traffic flow condition is oversaturated.
Highlights
Roundabouts have become a very common form of intersection control in many countries since the modern design was developed in the U.K. in 1966 [1]
One turbo roundabout variant was implemented, the basic turbo roundabout that includes double-lane entries and double-lane exits on major approaches, while it has double-lane entries and single-lane exits on minor approaches, all along with two circulatory lanes. e current study evaluates a high-volume three-lane conventional roundabout with three lanes on major approaches, dual entry lanes on minor approaches, and three full circulatory lanes, which has not been studied before. e study is an attempt to investigate the effect of converting a high-volume conventional roundabout into a turbo roundabout
Turbo roundabouts have never been built in Qatar, where aggressive driving behavior is very common especially in high traffic conditions. e turbo design offers high capacity and lowers vehicles delay in many European countries due to its unique features such as spiral road markings and raised lane dividers
Summary
Roundabouts have become a very common form of intersection control in many countries since the modern design was developed in the U.K. in 1966 [1]. Even though multilane roundabouts o er higher capacity, as compared to single and mini-roundabouts, they create more cut-o and weaving points due to lane changing behavior of drivers when entering, circulating, and exiting such roundabouts [2]. E lower values of follow-up headways and/ or critical gaps result in higher capacity at intersections whose tra c operation is mainly determined based on gap acceptance such as roundabouts and led to the conversion of some roundabouts to signalized intersections in these countries [10]. A decision was made to convert the roundabout into a signalized intersection since the turbo design is still new and not a common alternative in Qatar.
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