Influence of Roundabout Inscribed Circle Diameter to the Traffic Safety

Abstract

The article presents an interesting result of research aimed on traffic safety of roundabouts. The relationship between the inscribed circle diameter of roundabout and the crash rate in the roundabout is presented. There is a certain optimal size of roundabout inscribed circle diameter identified for safe operation.

Reliability of stopping and decision sight distance at roundabouts

“…The geometric features that affect the safety and capacity of roundabouts include the entry lane width, the number of entry lanes, the rate of deflection for the entry and exit legs, the circulating lane width, the radius of the central island, the flare length, and the radius of the inscribed circle. Mahdalova et al (2013) claim that drivers will traverse the entry curves of roundabouts at a lower speed if all of the geometric features are well designed. The geometric elements of roundabouts are illustrated in Figure 2-4.…”

“…Table 2.2 shows common design vehicles considered for roundabouts and their corresponding required inscribed circle diameter. Mahdalova et al (2013) evaluated the effect of the inscribed circle radius on the safety of roundabouts. The results of their analysis revealed that increases in the radius of the inscribed circle reduce the rate of collisions.…”

“…After reaching a certain inscribed circle radius, the crash rate increases as the inscribed circle radius increases. According to Mahdalova et al (2013), a large inscribed circle radius increases the vehicle speed which in turn increases the frequency of collisions. On the other hand, if the radius of the inscribed circle is very small, it is necessary to increase the width of the circulatory roadway in order to accommodate the design vehicle.…”

“…Since a small inscribed circle diameter with a wide roadway does not force the vehicles to reduce their speed, vehicles would traverse the circulatory roadway in almost a straight line, increasing the crash rate. Mahdalova et al (2013) claim that 20 m is the desired inscribed circle radius for the safety of single-lane roundabouts. The raised, circular, and non-traversable area of roundabouts is called the central island.…”

Safety and Efficiency Analysis of Turbo Roundabout with Simulations Based on the Lujiazui Roundabout in Shanghai

“…Over the past 20 years, scholars have conducted relatively in-depth and thorough studies on roundabouts in terms of traffic safety and efficiency using different approaches. Mahdalova et al [25] presented the relationship between the inscribed circle diameter of a roundabout and the crash rate. Furthermore, Kim and Choi [26] developed a model to investigate the relationship between crashes and roundabout geometric characteristics to reveal major geometric elements of roundabout safety.…”