Accommodating Oversize/Overweight Vehicles at Roundabouts: Survey Results and Preliminary Designs

There is considerable evidence that roundabouts are the safest most efficient form of traffic control for most intersections. The potential use of roundabouts with all their inherent benefits may be greatly diminished because they may not be able to accommodate oversize/overweight (OSOW) vehicles sometimes called “Superloads”. To use these OSOW vehicles as a design vehicle for roundabouts would be very costly and inefficient, and more importantly, negate the benefits of roundabouts which rely on being designed to operate at slower speeds from adequate deflection. Large roundabouts with little deflection and wide lanes would encourage higher speeds which would likely reduce the safety benefits. The problem, therefore, is how to accommodate OSOW vehicles without sacrificing the integrity, safety and other benefits of roundabouts. The objective of the study was to survey and compile current practice to fill in gaps in knowledge on the effects that OSOW vehicles have on roundabout location, design, and accommodation. The secondary objective of this study includes using design software such as TORUS and Autoturn to show the effects of OSOW on a prototype single lane roundabout and a prototype double lane roundabout to illustrate things that need to be considered for the types of design modifications that may be necessary to accommodate OSOW vehicles at roundabouts. A Total of 4 surveys have been conducted (2 successfully completed, 1 with very limited success and 1 in progress which is expected to be very informative) with U.S State DOTs and OSOW Haulers, and personal interviews with Roundabout Design Consultants to compile various issues like bottle necks on the highway system, problems of OSOW vehicles on state’s highways and specifically at roundabouts, possible design issues and mitigation strategies. This writing is primarily from the results from the first 2 surveys conducted with the 50 U.S States and preliminary designs to mitigate OSOW problems at roundabouts.