City of Kent to install roundabout on 108th Avenue SE

The city of Kent plans to build another roundabout, this one on the East Hill.

The City Council approved March 2 to accept a state Department of Transportation grant of $885,000 toward the $900,000 project at the intersection of 108th Avenue Southeast and Southeast 264th Street. The city must pay $15,000 in matching funds, which will come from the city’s B&O tax revenue.

Construction is expected to be finished by December 2022, according to city documents.

Crews would convert the existing stop-controlled intersection to a compact roundabout, which features one lane and will be about half the size of the recently completed roundabout at Fourth Avenue South and Willis Street near downtown Kent that replaced traffic signals.

A compact roundabout also features no landscaping and about a 3-foot high curb so large trucks can mount the curb to navigate through the roundabout. Large trucks from nearby Home Depot and Target stores may need to use the new roundabout.

Erik Preston, city traffic engineer, told the council at its Feb. 23 virtual Committee of the Whole meeting that the funds are from the Highway Safety Improvement Program, federal monies administered by the state. State traffic engineers selected the project due to a serious injury crash in 2016 at the intersection. The federal program targets road safety projects that have had serious injury crashes in the last five years.

The intersection has no pedestrian crossing. The roundabout will allow pedestrians to cross.

“Roundabouts reduce serious crashes,” Preston said. “They also have a calming effect because every vehicle must slow down.”

The city applied for the grant in 2020. The Highway Safety Improvement Program distributes funds every two years. The state awarded the grant in December to Kent. If the city fails to award a construction contract by April 2023 for the roundabout, it must come up with a matching grant of $90,000 rather than $10,000.

Roundabout benefits

Roundabouts reduced injury crashes by 75% at intersections where stop signs or signals were previously used for traffic control, according to a study by the Insurance Institute for Highway Safety (IIHS). Studies by the IIHS and Federal Highway Administration have shown that roundabouts typically achieve:

• A 37% reduction in overall collisions

• A 75% reduction in injury collisions

• A 90% reduction in fatality collisions

• A 40% reduction in pedestrian collisions

There are several reasons why roundabouts help reduce the likelihood and severity of collisions, according to the state Department of Transportation and national studies:

• Low travel speeds – Drivers must slow down and yield to traffic before entering a roundabout. Speeds in the roundabout are typically between 15 and 20 mph. The few collisions that occur in roundabouts are typically minor and cause few injuries since they occur at such low speeds.

• No light to beat – Roundabouts are designed to promote a continuous, circular flow of traffic. Drivers need only yield to traffic before entering a roundabout; if there is no traffic in the roundabout, drivers are not required to stop. Because traffic is constantly flowing through the intersection, drivers don’t have the incentive to speed up to try and “beat the light,” like they might at a traditional intersection.

• One-way travel – Roads entering a roundabout are gently curved to direct drivers into the intersection and help them travel counterclockwise around the roundabout. The curved roads and one-way travel around the roundabout eliminate the possibility for T-bone and head-on collisions.