Roundabouts have become commonplace in numerous locations across the globe; however, they are relatively new in Alberta. Experience has shown marked improvements in safety and efficiency, and thus roundabouts have become an ideal option over signalized intersections or other intersection improvements. Additionally, their operation and maintenance costs are typically lower than for signalized intersections. However, in Alberta, there are concerns that current roundabout construction costs are high in comparison to alternate options. Numerous commercial loads, including oversize and overweight (OSOW) vehicles, use Alberta’s highway corridors on a daily basis. The department’s intent is to maintain a highway system that will have no blockages for high loads or oversized loads. Roundabouts may present a bottleneck if OSOW loads are not considered. This problem can be addressed by constructing wider approaches and/or using wide aprons; yet this comes at a cost for construction and may adversely affect operations by regular traffic due to higher speed entries. Another strategy is to make the centre island completely traversable with removable signs. However, situations such as these may present higher costs than anticipated. The department has identified potential high cost factors, including: traffic accommodation during construction, size of inner circle and overrun areas and the required amount of concrete, design life, etc. There is a general consensus that the cost will decrease once roundabouts become less unknown to contractors, as presently they are not accustomed to roundabout construction. The department aims to determine best design practices for roundabouts with the most cost-effective solution. For example, one good design practice is to build a roundabout that works for current volumes plus a reasonable time period (i.e. 10 years), and then be prepared to add additional lanes if required. Aside from saving cost, this practice is safer and allows drivers to adjust to a simpler roundabout. Costsharing formulas have also been proposed to finance the roundabout. For the purposes of this paper, a comparison of construction practice and resulting costs of existing roundabouts will be presented. Information on roundabout practices in other jurisdictions, with a focus on the accommodation of OSOW loads, will be obtained through comprehensive literature review and communication with professionals. The main intent of this paper is to identify potential improvements to current roundabout design and construction and to provide recommendations on the most efficient solution that maximizes safety while being fiscally acceptable.
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