Performance checks as prerequisites for environmental benefits of roundabouts

Environmental benefits of roundabouts are well known: roundabouts help reduce fuel consumption and vehicle emissions and also require less maintenance than traditional intersections with traffic signals, providing a reduction in energy use and costs. The prerequisite for these assets is smooth speed profile through the roundabout, which is achieved by ensuring the clarity of the situation for approaching drivers, visibility between road users, comprehensibility of traffic operations and appropriate accommodation of the design vehicles. These requirements are met through quality roundabout design. Roundabout design is an iterative process that consists of identification of initial design elements, performance checks (definition of fastest path, offtracking geometry and visibility tests) and final design details. The development of reliable software for vehicle movement simulations simplified these performance checks, and led to the exploration of new possibilities for roundabout design, which represents a logical step in the area of road traffic engineering research. In Croatia the positive aspects of roundabouts are often annulled due to their inappropriate design. Namely, performance checks that should ensure proper speed profile and required intersection visibility are usually ignored. The main reason for this stems from the fact that there are no official national guidelines or regulations for the roundabout design. In this paper key elements for successful roundabout design will be shown, based on performance checks conducted by vehicle movement simulation software. Proposed instructions could be used for the development of national guidelines for roundabout design.