Transforming a Traditional Intersection into a Roundabout: Improving Traffic Flow and Safety

Transforming a Traditional Intersection into a Roundabout: Improving Traffic Flow and Safety

Roundabouts are becoming a popular solution to improve traffic flow and safety at intersections. Unlike traditional stop-controlled or signalized intersections, roundabouts keep traffic moving in a circular pattern, reducing congestion and accidents. But how do you convert a traditional intersection, like a four-legged, two-way stop, into an efficient single-lane roundabout? Let’s take a look at the process.


Why Roundabouts?

Roundabouts are circular intersections that use yield control at entry points, with traffic flowing in one direction around a central island. The modern roundabout design, developed in the UK in the 1960s by engineer Frank Blackmore, has been proven to reduce delays, lower accident rates, and improve traffic flow compared to traditional intersections.


Assessing the Need for Change

In our case study, the intersection was a four-legged, two-way stop, which created long delays and inefficient traffic flow. To assess the best solution, we conducted background studies—including traffic surveys, geographical analysis, and zoning reviews—and performed roundabout analysis using analysis tool and an Intersection Control Evaluation (ICE). The ICE analysis showed that a single-lane roundabout would effectively resolve the traffic issues at this location.


Designing the Roundabout

Once the roundabout solution was confirmed, the design process began. We focused on the centrelines, central island, entry and exit lanes, and splitter islands, all while adhering to local criteria. The roundabout geometry was finalized, and we worked on grading and aligning the roadway to seamlessly integrate with the existing infrastructure.


Drainage solutions like ditches and pipes were included, along with utility relocations (gas lines, water mains, etc.). A mill and overlay section was also planned to ensure smooth connections with the existing road.


Finalizing the Design

With the geometry and surface design complete, we added traffic markings such as yield lines, lane dividers, and circular markings. Key traffic signs—yield signs, roundabout signs, and circular intersection signs—were also incorporated for driver safety. The final design was documented in a comprehensive set of construction plans.


A Key Lesson: Thorough Site Evaluation

During utility planning, we discovered discrepancies in the location of existing gas lines, which fell within the roundabout’s footprint. This oversight was caught only after a revised survey. It highlighted the importance of thoroughly reviewing existing site conditions to avoid costly rework and ensure the design remains cost-effective.


Conclusion

Converting a traditional intersection into a single-lane roundabout can significantly improve traffic flow and safety. Through careful planning, analysis, and design, roundabouts provide a modern solution to outdated intersections, offering smoother, safer driving for everyone on the road.