Lambton County, located just east of Sarnia, Ontario, retained CIMA+’s expertise to address safety concerns at the intersection of Egremont Road (County Road 22) and Nauvoo Road (County Road 9), where several injury collisions and a fatal crash had occurred.
In the first phase of the project, CIMA+ conducted an intersection control study to evaluate four alternatives:
- Maintaining the existing two-way stop
- Implementing an all-way stop
- Installing traffic signals
- Constructing a single-lane roundabout
The roundabout, although more expensive to construct than traffic signals at the intersection, provided superior operational and safety performance compared to both signals and stop control. Life cycle costs were comparable due to lower operations and maintenance costs, as well as a lower societal cost resulting from reduced collision frequency and severity. Agencies like the Ministry of Transport Ontario (MTO) assign costs to motor vehicle collisions to accurately prioritize funding for safety improvements. Typical societal costs are $8,000 for a propertydamage-only collision, $60,000 for an injury collision, and over $1 million for a fatal collision. As a result, the County approved the roundabout for construction.
Enhancing safety and functionality for small and large vehicles
CIMA+ was later asked to complete the detailed design. This primarily involved refining and optimizing the conceptual design developed during the intersection control study to maximize capacity and safety performance. Because Egremont Road is on an emergency detour route (EDR) for Highway 402, the geometric modifications included dual outer truck aprons and a two-height central island apron to accommodate large vehicles, including long combination vehicles or trucks pulling two full-length 53-foot trailers.
Further modifications were made to the geometric design of the roundabout within tight deadlines in response to unanticipated utility conflicts. Finally, our team developed custom guide signage for the roundabout and performed a review of grading and pavement elevations, as well as lighting and landscaping.
Dual truck aprons are specially designed paved areas on the outer edges of the roundabout and around the central island. They provide extra space for large vehicles—such as trucks with one or two trailers—to safely complete turning movements without encroaching onto the grass-lined boulevards or landscaped central island. These aprons are raised and textured to discourage drivers of smaller vehicles from using them, but are strong enough to support the weight of heavy trucks. Dual-apron configurations are relatively new at roundabouts but offer greater flexibility in accommodating different-sized vehicles and turning paths, all while maintaining low speeds for smaller vehicles and maximizing safety for all users.
This tailored roundabout design meets EDR requirements for Highway 402 and marks a significant improvement in safety and traffic flow at the intersection.