Kiertoliittymillä

Kierroliittymillä (Finnish: “roundabout” or “traffic circle”) is a type of traffic intersection designed to smooth the flow of vehicles by providing a free‑flowing circular lane around a central island. Vehicles enter the circle from any approaching direction and keep moving clockwise (or, in a few cases, counter‑clockwise) until they reach the exit that merges them back into the main road. The design eliminates conflict points that would normally occur at a conventional four‑way intersection, thereby reducing the likelihood of high‑severity collisions.

In Finland and many other European countries, kiertoliittymillä are used primarily for medium‑ to high‑volume roads, including urban arterials, regional highways and rural main roads. The Finnish Road Administration (Mieli) provides a technical standard for the geometry of roundabouts, specifying lane widths, curvature radii, entry angles, and signage. Typical lane widths for vehicles and bicycles are 3.5 metres and 2.5 metres respectively, while pedestrian crossings are situated along the perimeter of the central island.

Benefits reported by traffic engineers include lower vehicle speeds, reduced number of red‑light running accidents, and decreased maintenance costs since the highway surface is less damaged by heavy traffic. Critics argue that roundabouts can cause confusion among drivers unfamiliar with the system, especially when signalised bus bays or multiple entry lanes are present.

Notable Finnish examples include the N7 roundabout at the intersection of Vantaa and Taloja, the Kivenlahti circular junction on the E18 in western Finland, and the small village‑type circles scattered throughout the countryside. These structures illustrate the practical application of kiertoliittymillä in balancing efficiency, safety and local traffic needs.