As cities continue to grow, the need for safe and efficient relief from traffic congestion continues to be a priority. One solution our Southeast region teammates often deliver is the construction of roundabouts. While many people have seen or experienced roundabouts, few understand how they work and how they benefit the public, and clients like the North Carolina Department of Transportation (NCDOT).
A roundabout is a circular roadway intersection with one-way traffic merging and travelling in the same direction around a central point. Roundabouts are often confused with their earlier cousin, the traffic circle, or rotary. Traffic circles were built in the U.S. from the early 1900s through the 1950s, and like roundabouts, traffic circles contained landscaped centers with intersecting streets. However, traffic circles allowed high speed merging, and as traffic increased over the years, so did accidents. The modern roundabout emerged in the United Kingdom in the mid-1960s as a solution to the problems of the traffic circle.
Modern roundabouts are designed for slower speeds, typically less than 30 mph, and must meet the needs of all users, including drivers, pedestrians, pedestrians with disabilities and bicyclists. “Roundabouts are generally more efficient for intersections with moderate traffic volumes,” explains Alex Wiseman, PE traffic engineer with STV Engineering, Balfour Beatty’s design partner on the US 70 James City project. “Instead of waiting at a red light, drivers enter a roundabout when it is safe to do so after yielding to other vehicles, pedestrians or bicyclists. If there are none, drivers are free to enter the roundabout by slowing down—but not coming to a complete stop.”
NCDOT manages more than 500 roundabouts across State of North Carolina, the most of any state in the nation. The state transportation agency understands that slowing down traffic in intersections directly correlates to fewer accidents and has invested in this solution to safeguard both state residents and visitors.
According to a study conducted by NCDOT, total crashes decreased 46%, fatal and injury crashes decreased 75% and frontal impact crashes decreased 76% after roundabouts replaced 13 signalized intersections with 55 mph speed limits.
In addition to increased safety, roundabouts help NCDOT make the most of their annual budget. Roundabouts require less right-of-way, which lowers the cost of land procurement, and have lower construction and maintenance costs. They also require little to no traffic signals, which provides a continuous flow of traffic around an aesthetically pleasing center. Although most of the state owned roundabouts have a simple grass island, the islands can also be designed with landscaping or other features to reflect the communities they serve.
Balfour Beatty’s Southeast teammates have partnered with NCDOT to use roundabouts to provide effective roadway solutions for North Carolina projects, including the award-winning Surf City Bridge Replacement project, completed in 2018, and the US 70 James City design-build project, currently under design. The purpose of the James City roundabouts is to improve traffic flow on a 5.1-mile stretch near New Bern.
“Through the use of roundabouts, the James City Design-Build team has eliminated 10 signals, which will reduce both the cost of constructing the intersections and long-term maintenance," explains Josh Sommer, PE project manager. "The roundabouts will also help make the area more resilient to power outages caused by inclement weather.”
The original design for the US 70 James City project included signalized intersections at all five interchanges. Due to the compact nature of the interchanges and the close proximity of the ramps to the underpasses, the team identified roundabouts as a safe, efficient alternative to signalized intersections.
After analysis and identification of the type of roundabouts that would serve the needs of the project, the design team submitted the designs as Alternative Technical Concepts (ATCs), and the project proposal documents were modified to install the roundabouts at intersections where traffic signals were originally proposed.
The US 70 James City roundabouts will efficiently and safely move traffic and help maintain easy access to local businesses that rely on the highway. One of the roundabouts will also reduce and may even eliminate substantial impacts to an existing adjacent railroad crossing.
Construction on US 70 James City is expected to begin early 2021.