Roundabouts are designers’ choice

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Turn east from the I-5 at Oceanside into the hills of Southern California and you’ll find the proposed location for a unique multiuse development project. The Lilac Hills Ranch project is a proposed mixed-use, pedestrian-oriented, sustainable community set on 608 acres. When completed in 2015, there will be 1,746 residential units along with retail spaces, community centers, parks and protected wetland habitat areas to enhance the livability of the area.


The vast tract of land will be connected by a network of roadways designed to accommodate pedestrians, cyclists and vehicles at reduced speeds. The Accretive Group of San Diego planned the community with pedestrian safety high on their priority list. To achieve this, Randy Goodson, Simon Malk and their colleague Jon Rilling needed traffic-calming features that fit with the overall design of the project, and roundabouts were one feature that came to mind.


“Accretive places strong importance on providing a safe, pedestrian-friendly neighborhood and town center,” said Malk. “Roundabouts were considered from day one because of their numerous safety and traffic-control benefits.”


Rebecca Ferguson of Landmark Consulting in San Diego took on the grading and road design part of the project. “Roundabouts are a new concept for Southern California,” said Ferguson. “It’s not like there are no roundabouts in San Diego at all, but this is definitely a new concept. It’s a relatively new thing for the county as well, and they are definitely open to it. They understand the benefits of roundabouts, and they are excited about it, and we’re going through the peer review process soon so the designs can meet their approval.”


Any engineer will tell you there is more to roundabout design than making cars go in a circle. Engineers have to determine the roundabout capacity requirements, and all roundabout designs must meet NCHRP 672 and FHWA requirements. It was a process that Ferguson learned on the job, but Torus is user-friendly, so she picked it up quickly.


“I had no experience with Torus,” said Ferguson. “I had done roundabout designing in Australia, but I hadn’t used software to do it. It was really nice to be able to use something that makes designing a lot easier. I needed to know how to keep the design within the FHWA rules, but also minimize the amount of right-of-way that I'm taking away from the developer. I figured out the iterative process and found that it was very fast. It took me about a day to figure out how to use it.”


Using Torus, design vehicles and movements are defined at the start and geometric elements are dynamically adjusted to accommodate the vehicle swept paths at all stages of the roundabout design. It enabled Ferguson to make her client happy and achieve an aesthetically pleasing design.


“The developer is a big fan of roundabouts because of the traffic-calming effects and the ability to make the landscaping look really nice.”

  • Transoft Torus roundabout
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