Residents of Carmel, Ind., are going around in circles – deliberately. In fall 2010, construction of six new roundabouts was completed in this bustling city immediately north of Indianapolis, bringing the grand total of Carmel roundabouts to 80. The new roundabouts give more street cred (pun absolutely intended) to its unofficial moniker as Roundabout Capital, USA.
But there is something different about Carmel's latest set of roundabouts. In this city – ironically the home of one of the country's first traffic signals, a device that roundabouts render unnecessary – the new roundabouts are elevated and proceed in more of a teardrop shape. The roundabouts are the design of American Structurepoint Inc., an Indianapolis-based multidisciplinary consulting firm.
All about roundabouts Roundabouts are road intersections that conduct traffic in one direction around a central island. Used in place of stop signs and traffic signals in many countries, roundabouts are relatively new additions to most roadways in the United States.
Drivers entering roundabouts must negotiate a sharp initial curve, reducing their travel speeds. Roundabout traffic enters or exits only through right turns, eliminating more dangerous left turns. In fact, the Insurance Institute for Highway Safety reported that motor vehicle crashes drop by approximately 40 percent with roundabout intersections, and crashes involving injuries drop by about 80 percent.
Carmel's Keystone Parkway In Carmel, one of the city's most heavily traveled roads is the Keystone Parkway (formerly known as Keystone Avenue/SR 431). Built in the late 1960s, this four-lane, divided state roadway was burdened with seven at-grade signalized intersections.
"Carmel has grown substantially in the past decade, and so has traffic on this roadway," explained Cash Canfield, P.E., a vice president of American Structurepoint. "The roadway formerly averaged 200 accidents per year, and a level-of-service analysis of its at-grade intersections received very poor marks."
In addition, the heavily traveled road essentially bisected the town, restricting all east-west movement of vehicles, pedestrians, and bicyclists.
To relieve traffic along the corridor, the Indiana Department of Transportation (INDOT) initially planned to add a third lane in each direction, with turn lanes at each of the intersections. Construction was slated to begin in 2008. The plan required removal of a number of existing buildings and the purchase of additional rights-of-way.
"Although the widening would have reduced congestion in the short term, the city was concerned that the plan would not provide a long-term traffic solution and might actually worsen the situation for local traffic and pedestrians," said Canfield. "City engineers and officials wanted the road lowered, with roundabout interchanges at each major cross street to provide safer intersections and increased mobility, eliminating both the visual and physical barriers the roadway caused."
In fact, for more than a decade, the city and the state of Indiana discussed relinquishing control of the corridor to Carmel. In 2007, the state decided to turn Keystone Avenue over to the suburb, which then partnered with American Structurepoint to refine and implement its vision for the renamed Keystone Parkway.
Designing a better intersection With the city of Carmel as the governing authority, the project ignited with a planning effort and the conceptual design of a four-lane expressway, including grade-separated, full-access interchanges at six points along a five-mile stretch of the most heavily traveled part of the road. American Structurepoint studied the feasibility of lowering portions of existing roadway and evaluated a variety of interchange configurations and geometries to understand the effect on adjacent properties.
Teardrop roundabout designs quickly emerged as an attractive alternative. American Structurepoint used Autodesk software – AutoCAD Civil 3D and its predecessor AutoCAD Land Desktop – to create intelligent 3D models of the innovative configuration, using road alignment and real traffic pattern data to help illustrate the ability for the unique configuration to meet public needs. American Structurepoint also used AutoCAD Land Desktop software to create 2D side-by-side displays of other interchange alternatives, such as tight diamond and single-point urban interchanges, to help demonstrate the impact of each alternative on the general environment and surrounding properties.
"Designing and visualizing a complex project in 3D not only helps accelerate the planning and design process, it also produces a higher-quality design," said Canfield. "There's just no comparison between experiencing your design in a 3D model versus looking at it on 2D plan sheets."
American Structurepoint used Autodesk 3ds Max Design software to visualize comprehensive traffic operations analyses, helping them determine whether the designs could work effectively for both current and projected traffic volumes. The firm imported their design models into 3ds Max Design and created near-photorealistic visualizations to better explore the design options.
"Then we used real traffic counts to help calculate the amount of vehicles that would be using the roadway and interchanges in the year 2025," said Canfield. "By importing this traffic data into 3ds Max Design, we created animations that simulated the projected traffic flow for these interchanges to evaluate how they function from a capacity standpoint."
As the design progressed, the teardrop roundabout clearly emerged as the most effective choice for the new interchanges. Not only did the traffic simulation help demonstrate that the tight configuration could handle projected traffic, the configuration also had a smaller project footprint, minimizing the impact to adjacent property owners.
Communicating the design "Although numerous roundabout interchanges have been constructed in the United States during the last several years, the teardrop roundabout design was definitely unique," Canfield said. "It was the first double-roundabout interchange in the state of Indiana, and no other state or municipality in the country had integrated roundabouts into an interchange design with such a tight configuration.
"The use of an intelligent, 3D model-based process on this project proved very effective for helping to communicate the design option to city officials and the public," Canfield said. "Instead of displaying construction documents, we used our model-based simulations to help visually sell the project. Through an aggressive public outreach campaign, we let everyone virtually 'test drive' the new road and roundabouts. That way, we could show business owners, elected officials, and the general public how the new interchanges would look, how they would blend into their surroundings, and how they would operate once they were installed."
"The 3D visualizations proved to be an invaluable tool for the city of Carmel to use in our outreach efforts," said Michael McBride, city engineer for the city of Carmel. "Developing more realistic animations of each and every interchange helped the citizens of Carmel see what the end product was going to look like, and how it would function upon completion. Citizens quickly became excited about the proposed corridor improvements because they were able to visualize the benefits the project could offer."
Greener infrastructure In addition to addressing capacity and safety concerns, the team at American Structurepoint also was able to design a sustainable, low-impact project. Using intelligent infrastructure models, the firm's engineers worked diligently to develop and promote a plan that did not require the disruption of any homes. "In the end, only one commercial building had to be relocated," reported Canfield. "Had we used a tight-diamond design, dozens of homes, businesses, and churches at each interchange would have been relocated."
Traffic now flows more freely, without the need for any traffic signals on the Parkway itself or in the interchanges. "The removal of traffic signals through the corridor reduces electricity consumption and motorists' emissions are lower because there's no longer any need for frequent starting, stopping, and idling," Canfield said.
Summary Construction of the Keystone Parkway project began in 2008 and was completed by the end of 2010. Overall project cost was $112 million – significantly less than the original estimate of $143 million.
"One of the project's main goals was improving safety and access for pedestrians and bicyclists," said Canfield. "The new roundabouts have added substantial capacity, connectivity, and safety for all modes of transportation. In fact, within a few months of the roadway's reopening, city officials reported a 78-percent reduction in personal-injury accidents at these intersections."
The project has created a sustainable transportation system to benefit the city for years to come. With no traffic signals, north-south traffic now flows more freely, and six new teardrop roundabouts capably manage east-west traffic over the Parkway. "Overall, the design proved so effective that INDOT is considering the teardrop configuration for future projects," Canfield said.
From American Structurepoint's perspective, design modeling was essential for the success of the project. "The ability to visualize our design, and then communicate that vision to all the project stakeholders, was the true value of design modeling on the Keystone Parkway project," said Canfield. "Without that vision, this project would not have become a reality."
Karen M. Weiss, P.E., is marketing manager AEC Industry – Transportation and Land for Autodesk. Craig Parks, P.E., is a project manager for the American Structurepoint Transportation Group.
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