Large vehicles

Roundabouts should always be designed for the largest vehicle that can be reasonably anticipated (the “design vehicle”). For single-lane roundabouts, this may require the use of a mountable apron around the perimeter of the central island to provide the additional width needed for tracking the trailer wheels. At double-lane roundabouts, large vehicles may track across the whole width of the circulatory roadway to negotiate the roundabout. In some cases, roundabouts have been designed with aprons or gated roadways through the central island to accommodate oversized trucks, emergency vehicles, or trains.