A Roundabout Way of Reducing Accidents

38 D+D FEBRUARY 2015 Q+ Got a concrete problem? Concrete A Ask the experts: [email protected]. By Todd Scharich, American Society of Concrete Contractors hen the Winnipeg Sun ran a page-three article in 2013 stat- A Roundabout Way of Reducing Accidents ing that the city, in Manitoba, Canada, planned to institute a Decorative concrete plays a ‘roundabout’ role series of roundabouts, reader in making America’s roads safer. reaction was immediate and W vociferous. mize delay and maximize traffic safety — problem because they don’t force drivers to “If you want to drive just like they do in and they do. slow down, as modern roundabouts do. London, move there!” one reader wrote. According to the Insurance Institute for They often have landscape or water fea- Another reader was concerned that Highway Safety, studies have found reduc- tures that can distract drivers. snowy conditions would create huge pile- tions in injury crashes of 72-80 percent and Another major difference is that in some ups as vehicles slipped while navigating reductions in all crashes of 35-47 percent at traffic circles, right-of-way priority is given the circles. “Those circles are in cities with U.S. intersections converted to roundabouts to vehicles entering the circles, while mod- warmer climates, what moron decided to from traffic signals or stop signs. ern roundabouts give that priority to vehi- initiate this farce!” the reader wrote online. One study of 19 rural roundabouts con- cles already in circulation. The newspaper article turned out to be verted from intersections with speed limits Because of these features, older traffic an April Fools’ Day prank, but it illustrates of 40 mph or higher, that originally had stop circles are prone to congestion and other common attitudes toward this relatively re- signs on the minor approaches, found a 62- problems absent from modern roundabouts. cent development in highway safety — at percent reduction in all crashes and an 85- Confusion between the two may play a part least before people experience them. percent reduction in injury crashes.1 in public attitudes concerning roundabouts, The U.S. has seen a dramatic increase in attitudes that usually change as drivers be- the use of roundabouts since 2000, and the Not Your Grandpa’s Traffic Circle come familiar with them.2 use of decorative concrete is a primary de- Modern roundabouts differ from old-style sign feature in them. traffic circles or rotaries in both design and Anatomy of a Roundabout Modern roundabouts are engineered to function. Older traffic circles have bigger Modern roundabouts are composed of a accommodate high volumes of traffic, mini- inner radiuses of 300 to 600 feet. That’s a circulating roadway surrounding a central 39 Concrete Q+A island with radiuses of 100-150 feet. The relatively small radius helps slow traffic. Island design increasingly features decorative concrete flatwork as an aesthetically pleasing and structurally sound element. The island’s outer edge in particular, known as the truck apron, features decorative concrete to distinguish it as a correctional buffer between the road and the island. The truck apron is so named because, while it separates most vehicles from the central island, it provides extra turning- room for the back-ends of large trucks as they maneuver through the roundabout. In addition to being decorative, the truck apron must be built to withstand heavy truck traffic. Colored, or colored and textured “split- A truck hauling two trailers enters a roundabout in Marquette, Mich., in the state’s Upper Peninsula. If it ter” concrete islands increase safety by continues around in the left lane, the rear trailer will take advantage of the extra turning room afforded by using contrasting colors that alert drivers to the decorative concrete truck apron. Photo courtesy of DLZ Architects. slow down as they approach the round- (Left) Splitter islands help guide a driver into the circulation path of a newly built roundabout in northern abouts. They also help direct traffic flow. Michigan. Photo courtesy of DLZ Architects. Decorative concrete also directs pedes- (Top) This roundabout in Carmel, Ind., sometimes called the “Roundabout Capital of America,” features trian traffic across splitter islands and adja- stamped red concrete in a brick herringbone design, one of the most popular looks for decorative concrete in roundabouts. Photo courtesy of DLZ Architects. cent walkways. 40 D+D FEBRUARY 2015 A vehicle navigates the circulation path of a two- lane roundabout in South Bend, Ind. While most roundabouts are designed with matching truck aprons and splitter islands, this one uses turf on its splitter islands. Photo courtesy of DLZ Architects. systems, the U.S. 23 and Lee Road interchange corridor handles approximately 8,000 vehicles per hour. Traditional signal alternatives were found to have inadequate capacity, resulting in ex- cessive delays and potentially dangerous backups on freeway ramps, according to Mark Johnson, P.E. of MTJ Roundabout Engi- neering, the project’s design engineer. A double roundabout configuration at the southbound ramp terminals accommodates six entries and exits with minimal circulating flow, increasing intersection entry capacity and reducing crash potential. Such complex- ity renders the visual cues supplied by decorative concrete even more important. The decorative concrete elements help increase driver awareness by making center and splitter islands more visible and by focusing driver attention on the system’s navigational Decorative Concrete Design The combination of safety, aesthetics and cues. in Roundabouts cost has increased the use of etched sur- From basic colored concrete, to etched fin- Red stamped concrete in running bond or faces in all types of municipal applications ishes, to stamped surfaces, the combination herringbone patterns have been popular de- and pedestrian traffic areas, including of colors, finishes and textures allow for signs for roundabout truck aprons and walk- roundabouts. nearly unlimited design options. ways for many years. Alternative colors, such Many recent round- as browns and tans, and new patterns and about designs combine finishes like flagstone are also taking their decorative concrete styles. places alongside popular red stamped brick. A project by Michigan’s One of decorative concrete’s biggest Washtenaw County Road trends has recently found its way into round- Commission used a brown about design. Washed or etched “sand- flagstone and red brick scape” finishes enhance safety by creating a pattern on the four round- higher coefficient of friction that increases abouts at the U.S. 23 and slip-resistance compared to other decorative Lee Road interchange. finishes. The combination creates Color in etched surfaces appears more nat- a traffic flow that has been ural than in stamped surfaces because of the proven to keep traffic mov- exposure of sand or other aggregate in the ing even with the proxim- mix design. Engineers and architects may ity of a heavily traveled This close-up of the decorative concrete truck apron on a roundabout near also appreciate the fact that the etched sur- highway and a popular the University of Notre Dame, in Indiana, shows the popular red stamped faces cost only slightly more than colored outlet mall. brick design. Such aprons are usually 10-15 feet wide and serve as an concrete alone, and significantly less than One of the country’s extra emergency vehicle lane, most commonly for large trucks needing stamped concrete. most complex roundabout extra turning room. Photo courtesy of DLZ Architects. 41 Concrete Q+A This double roundabout at U.S. 23 and Lee Road near Ann Arbor, Mich., is one of the most complex in the nation, as it handles 8,000 vehicles per hour from two major roads and an interstate highway. Multiple colors and patterns of decorative concrete feature prominently in the design. Photo courtesy of MTJ Roundabout Engineering. Low-Cost Alternatives This expanding population has and will 3 U.S. and World Population Clock, Attempts to lower installation costs have continue to place extreme demands on the census.gov. led some designers to try brick pavers and U.S. road system. Modern roundabouts are 4 Our Growing Population, GP 60-1, p.1, U.S. stamped asphalt as alternatives to decora- one method of handling the ever-increasing Bureau of the Census, Washington, DC, tive concrete. volume of traffic. As the number of round- 1961. Brick pavers without a concrete base abouts grows — and a quick Internet search 5 U.S. and World Population Clock, can’t withstand high traffic volumes, while shows that nearly every state in the U.S. is census.gov. paver installations with concrete bases tend studying how to incorporate them — deco- to cost more than most decorative concrete rative concrete will continue to play an im- About the Author installations. portant part in roundabout design. The role Todd A. Scharich is the decorative concrete Stamped asphalt is not much cheaper of the decorative concrete industry is to specialist for the American Society of Con- than stamped concrete but must be coated continue to provide a durable end-product crete Contractors. He provides support to to achieve its color, which wears away with that engineers and architects can trust and their membership through the Decorative any traffic volume. will be proud to feature in their projects — Concrete Hotline, educational opportunities projects that reduce accidents and injuries and technical documents. Scharich has pre- More People Means More Traffic on American roads. sented at 11 straight World of Concrete con- Between births, deaths and immigration, ferences on both business and technical the U.S. population is growing by one per- Notes topics related to decorative concrete. D+D son every 16 seconds according the U.S. 1 “Roundabouts,” iihs.org, February 2014.

Load more