This paper builds upon one submitted for the 2009 conference that discussed “small” users (pedestrians and cyclists) and “large” users (trucks) of roundabouts. It covers the topic of large commercial vehicles at roundabouts in more detail. Several horizontal design treatments exist to accommodate large commercial vehicles at roundabouts. This paper examines the use of widened entries and exits, partiallytraversable truck aprons, gated pass-throughs, and right-turn by-pass lanes. Unlike single-lane roundabouts, no special geometric treatments are necessarily needed to physically accommodate large commercial vehicles at multi-lane roundabouts. However there are still a number of considerations in terms of lane use. This paper discusses whether to allow for trucks to overtrack adjacent lanes in a roundabout, and whether to install lane lines in the circulatory road. Two case studies are then used to describe recent projects undertaken in northern Alberta to accommodate one or more over-dimensional vehicles through a roundabout. The first case study summarizes the preliminary design of a multi-lane roundabout to accommodate an over-dimensional vehicle making a through movement at the intersection of Highway 63 and Highway 69 in Fort McMurray, Alberta. The second case study summarizes the preliminary design of a single-lane roundabout to accommodate several over-dimensional vehicles making turning movements at the intersection of Highway 55 and Highway 892 west of Cold Lake, Alberta. In both projects a number of the treatments described in this paper were employed to accommodate the vehicles without compromising the inherent safety benefits of the roundabout.
