Accommodating Vulnerable Road Users in Roundabout Design

Roundabouts, under the right circumstances, are quickly proving themselves to the North American transportation engineer as a viable intersection treatment for both urban and rural roadways. The design of roundabouts is a complex procedure involving several variables, which need to be addressed to ensure a design is safe and has adequate capacity. A principle based design approach that balances the competing objectives of safety, capacity, and cost allows the designer to achieve a good solution for a particular site. Ideally, these design principles provide the engineer the flexibility to tailor a design to meet differing needs. For example, a slower entry and/or exit speed for increased pedestrian safety, or surfacing treatments for the visually impaired, or geometric configurations promoting higher capacity. Because good design is not a one-size fits all approach, following a 'prescriptive' standard design methodology applied across the entire range of roundabouts will not result in balanced designs. Creating added confusion for designers is the fact that Europe, Australia, and the UK each have different sets of design principles, in some cases contradictory, which have evolved based on varying levels of research. Roundabouts have their own set of advantages and disadvantages when comparing pedestrian and cyclist treatments to those provided at conventional intersections. The literature shows, given a properly designed roundabout facility, that vehicular and pedestrian safety at roundabouts, is almost always improved when compared to conventional intersections. Results regarding cyclist safety are somewhat mixed. Due to the elimination of conflict points at roundabouts and the lower speed differentials compared to conventional intersections, accident severity for all users is often significantly reduced when collisions occur, although frequency may increase.