Modern and alternative types of roundabouts - state of the art

Over the recent decades, roundabouts have been increasingly used when building new at-grade intersections and up-grade junctions all over the world, and also when rebuilding existing intersections. Modern roundabouts exist in all European countries and mainly worldwide, so we can say that today modern roundabouts are a world phenomenon. No uniform guidelines exist in Europe for the geometric designing of roundabouts as specific circumstances (local customs, habits, traffic cultures...) differ from country to country. Certain solutions that are safe in one country could be dangerous in another. Consequently, most countries have their own guidelines for the geometric designs of roundabouts that are, as far as possible, adapted to their circumstances in these countries and are therefore more acceptable within their surroundings. Today, after many years of experience, there are different ideas about the "ideal roundabout", with some consensus on the crucial effect of rules how to negotiate intersections. There are several different types of roundabouts worldwide today, called the alternative types of roundabouts. Some of them are already in frequent use all over the world (hamburger, dumb-bell.), and some of them are recent and have only been implemented within certain countries (turbo roundabout, dog-bone.) or are still at the development phases (turbo-square, flower, target, with segregated left-turn slip lanes.). Both groups typically differ from the "standard" one-or two-lane roundabouts in one or more design elements, as their purposes for implementation are also specific. Therefore, it was decided that it would be useful to collate, in one article, some of the alternative types that are already in frequent use today in some countries and some of them that are " still coming".