Mini-roundabouts for Improving Urban Accessibility

Abstract

Mini-roundabouts belong to a specific class of the so-called modern roundabouts. As their name states, they have smaller geometric features than single lane standards roundabouts. Moreover, the inner central island of a mini roundabout is often surmountable or semi-surmountable by heavy vehicles engaged in left turning maneuvers. The field of application of the mini roundabouts is not very wide, usually it is restricted to the urban area. This is essentially due to their reduced geometric characteristics, and for this reason they are more effective where traffic flows have lower speeds and volumes. Nevertheless, mini roundabouts play an important role in traffic network design because the number of intersections is much higher in any urban area than in a rural one. From a general point of view, the advantages attained by a mini roundabout can be summarized in the road safety upgrade by lowering of vehicle speeds, the reduction of delays and queues, the road space general improvement and a better perception of intersection in the environment. Frequently, mini roundabouts might be applied to instances also well suited to be coped with single lane roundabouts, even if they differ from these last, both for lower construction costs, and lesser need of road surface. Therefore, a mini roundabout is better suitable and more efficient in an urban area, especially in a residential one, when some basic condition are matched: low traffic volumes and speeds, single lane converging roads, reduced intersection surface, few heavy vehicles, i.e. lorries and buses. The mini roundabout design must take into account the above requirements since planning operation through feasibility checks of basic warrants. High attention should also paid to requirements due to the limited tolerances imposed by geometry. Today, any designer has at his disposal and help the guidelines of many countries in the world report, in a more or less in-depth way, the design standards of the mini roundabouts. As always, it is clear that it is not enough to have good guidelines if you do not have the right knowledge to apply them. This document would aim to make an organic contribution to the knowledge improvement and practical planning and design of mini roundabouts.