Equipment World Digital Magazine
Issue link: http://read.dmtmag.com/i/732903
EquipmentWorld.com | October 2016 65 Roundabouts A roundabout on Missouri 13 in Johnson County. Missouri DOT R oundabouts, common in Europe, are making inroads for use in lower volume intersections. Roundabouts have been used for decades in other countries, perhaps most recognizably in the United Kingdom. The FHWA estimates that since the fi rst round- about was built in the United States in 1990, somewhere between 3,500 and 4,000 have been built in all 50 states and Washington, D.C. Traffi c fl ow in a roundabout is simple in concept, yet it seems to perplex many new to the intersections. In a roundabout, vehicles move counterclockwise, with incoming traffi c having the burden of yielding to vehicles already in the intersection. The design removes perpen- dicular crossings and turns going against traffi c, and creates an environment of merging at slow speeds. These intersections keep traffi c fl owing to reduce congestion and they have been shown to be safer than traditional intersections. The National Cooperative Highway Research Program estimates intersections that have been converted to roundabouts have a 35 percent reduction in total crashes and a 76 percent reduction in injury crashes. The benefi ts of a roundabout conversion are similar to that of DDIs – they're fast and cheap. An example is a project in Jackson County, Georgia, where the Georgia Department of Transportation installed a mini-round- about at the intersection of Georgia 11 and Georgia 124, both of which are two lanes. GDOT widened the approaches, added a central island, and repaved and striped the entire intersection for $63,000 over a few weekends in April 2013. The Missouri Department of Transportation's diverging diamond interchange at U.S. 65 and Battle- fi ed Road, completed in September 2015. The project recently won a 2016 award from the Mid-America Association of State Transportation Offi cials for Best Use of Innovation as part of the America's Transporta- tion Awards program. SECTIONS gives credence to the argument that intersection design needs a rethink. This is where interchanges, such as DDIs, fi t in. Their designs eliminate confl icting left turns needed to clear opposing traffi c, a feature that inherently improves safety and keeps traffi c fl owing. Diverging diamonds DDIs, also referred to as double crossover diamonds, have been built or planned in at least 29 states, which is signifi cant considering the fi rst one in the country