WSDOT installing compact roundabouts for I-5 interchanges

Bellingham, Wash. — The Whatcom County Council approved a plan for the Washington State Department of Transportation to install three compact roundabouts near the Interstate 5 interchange with Slater Road, between Bellingham and Ferndale. WSDOT recommended the compact roundabouts as a practical, low cost solution for the intersections after examining several options, including making each a four-way stop, installing traffic signals or adding full roundabouts. Four-way stops would create even bigger traffic back-ups, especially at peak hours. Signals or full roundabouts cost about $1.5 to $2.5 million each. Compact roundabouts can be built in the existing paved area for about $100,000 apiece.

The compact roundabouts will be located at the northbound and southbound I-5 ramps at Slater Road and at Pacific Highway and Slater Road.

The county will fund the $300,000 project, which will improve traffic flow and safety at the intersections, particularly for vehicles turning left. WSDOT will put the project out for contractor’s bids in the next week. Work should be completed by early fall.

“I’m pleased that we are able to provide this interim solution to the ongoing traffic challenge that we have at Slater Road,” Whatcom County Executive Jack Louws said. “This is such a great example of the strength of collaboration with local jurisdictions and state agencies, and I look forward to partnering on other projects in the future.”

WSDOT Mount Baker Area Assistant Regional Administrator Todd Harrison said he’s glad to work with Whatcom County on this practical design project, which will reduce the chance of serious collisions.

“This area has somewhat limited sight lines, so the compact roundabouts will help all traffic safely navigate the intersections,” Harrison said.

About compact roundabouts

Compact roundabouts are similar to full roundabouts because they use a raised center island to direction traffic flow. However, compact roundabouts have a smaller diameter – about 62 to 67 feet at these three intersections, compared to up to 120 feet for a full roundabout. Also, the center island of a compact roundabout is three inches tall, while a full roundabout’s center may be six inches or more, with a three-inch truck apron around the edge.

Most vehicles will go around the compact roundabout’s raised island, which will be paved with asphalt. The rear wheels of longer trucks and trailers may ride up onto the center island to help them through the roundabout.

The smaller size allows compact roundabouts to be built more quickly with less disruption to traffic. It should take about two weeks to complete all three compact roundabouts once work starts in September.