Potential for Metering to Help Roundabouts Manage Peak Period Demands in the United States

Abstract

Roundabouts generally provide safety and other advantages. During peak hours, however, even moderate demands on an upstream approach can result in long delays and driver frustration over downstream movements. A metering signal is one way to ensure that all demands at a roundabout are adequately served. A roundabout metering signal regulates flow into the circle from one approach and thereby creates larger gaps in the circle for downstream entrants. Although metering signals have been used successfully around the world, little guidance is available for U.S. designers. The goal of this research was to provide U.S. designers with some guidance on the use of metering signals. The authors developed a simple macroscopic model based on the Highway Capacity Manual, validated it by using a simulation model, and performed exercises with it on a number of demand combinations to see where a meter might help. The macroscopic model should be helpful as a quick screening tool. The results from application of the model provide evidence that a meter may reduce delays compared with those seen in an unmetered roundabout with some demands. Although signalized intersections produced lower delays than did metered or unmetered roundabouts in most cases tested, roundabouts were sometimes better. Analysts should consider more than just peak period delays in deciding on the optimum traffic control at an intersection. If, with the aid of a metering signal for a few peak hours, a roundabout produces slightly higher delay levels during those peak hours than a standard traffic signal, with consideration of its many other benefits, a roundabout could well be the optimum design.

Evaluating Operational Performance of Intersections Using SIDRA

“…They reported based on their case study that delay was reduced by 50% and number of conflict points by 34% compared to the existing configuration [11]. Hummer et al (2014) using a simple Highway Capacity Manual based macroscopic model evaluated where a meter might help to improve performance of a roundabout [12]. They found that signalized intersections generally produce lower delays than metered or unmetered roundabout in most of the tested cases.…”

Optimal Control of Connected and Automated Vehicles at Roundabouts: An Investigation in a Mixed-Traffic Environment

“…Roundabouts generally provide better operational and safety characteristics over other typical intersections; see Flannery and Datta (1997); Flannery et al (1998); Al-Madani (2003); Sisiopiku and Oh (2001). However, the increase of traffic may become a concern for roundabouts due to their geometry and priority system -even with moderate demands, some roundabouts can still reach capacity; see Hummer et al (2014); Yang et al (2004). Moreover, traffic from minor-road approaches may experience significant delay if the circulating flow is heavy.…”

“…Moreover, traffic from minor-road approaches may experience significant delay if the circulating flow is heavy. Previous research has focused mainly on enhancing roundabout mobility and safety with improved metering, or traffic signal controls, e.g., Hummer et al (2014); Yang et al (2004); Martin-Gasulla et al (2016); Xu et al (2016). These efforts investigate the potential of metering signals in improving roundabout operations during rush hours.…”

“…These efforts investigate the potential of metering signals in improving roundabout operations during rush hours. Hummer et al (2014) tested a metering approach for a single-lane and a two-lane roundabout models with different levels of approaching traffic demand. Martin-Gasulla et al (2016) studied the benefits of metering signals for roundabouts with unbalanced flow patterns.…”

Prediction of queuing length at metering roundabout using adaptive neuro fuzzy inference system

“…Under unbalanced traffic flow conditions, roundabouts are likely to experience long queuing problems. [6][7][8] The other studies on unbalanced traffic conditions were conducted and the unbalanced flow was defined through the origin-destination factor. 9,10 In addition, the origin-destination factor may improve the estimation of roundabout capacity, in particular, with the unbalanced traffic conditions.…”