SR 503 / NE Rock Creek Rd Intersection Improvements

This intersection was identified as an ideal location for a compact roundabout due to the number and severity of collisions observed during a five-year analysis period, between January 2013 and December 2017. Installing a compact roundabout provides the highest safety benefit to travelers by reducing the number and the severity of conflict points when compared to the existing configuration. In addition to this crash data, other factors that supported a compact roundabout design include:

• Average daily traffic less than 25,000 vehicles;
• Intersection is currently controlled with stop signs;
• Higher than expected crash frequency; and
• No requirement to purchase additional property.

Studies have shown that roundabouts are safer than traditional stop sign or traffic signal-controlled intersections.

Roundabouts reduced injury crashes by 75 percent at intersections where stop signs or traffic 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 (FHWA) have shown that roundabouts typically achieve:

• 37 percent reduction in overall collisions
• 75 percent reduction in injury collisions
• 90 percent reduction in fatality collisions

Q&A

Why a roundabout?
Modern roundabouts are near-circular intersections at grade. They are an effective intersection type with fewer conflict points and lower speeds, and they provide for easier decision making than other intersection types. They also require less maintenance than traffic signals. Well-designed roundabouts have been found to reduce crashes (especially fatal and severe injury collisions), traffic delays, fuel consumption, and air pollution. They also have a traffic-calming effect by reducing vehicle speeds using geometric design rather than relying solely on traffic control devices.

What is a compact roundabout? 
Compact roundabouts are a hybrid of attributes found in mini- and single-lane roundabouts. Similar to a mini-roundabout, a compact roundabout may require minimal additional pavement, has a completely mountable center island, and in many cases existing curb or sidewalk can be left in place. As a result, compact roundabouts rarely require the purchase of right of way. Compact roundabouts are similar to single-lane roundabouts regarding design vehicle assumptions, ability to process traffic volumes, and signing. Learn more about the types of roundabout WSDOT considers (PDF 1.8KB)

I didn’t personally witness any crashes, what crash data did you collect? 
Between January 2013 – December 2017, 64% of the 14 crashes at this intersection were at-angle collisions. Traffic data from this five-year period showed:

• 1 fatality collision
• 1 disabling (serious) injury
• 0 non-disabling (evident, minor) injury
• 5 possible injuries
• 7 collisions that resulted only in property damage

Since 2018, WSDOT has observed an increasing trend of at-angle crashes at this intersection. 77% of crashes at this intersection in this time-period were at-angle crashes.  From a total of 9 crashes, traffic data shows:

• 1 disabling (serious) injury
• 1 non-disabling (evident, minor) injury
• 1 possible injuries
• 6 collisions that resulted only in property damage

WSDOT collects crash data from law enforcement following a crash the same way as all other states. Crashes are categorized using the KABCO scale (PDF 335KB) based on guidelines established by the Model Minimum Uniform Crash Criteria.

Why did you not consider a signal at this location? 
The history of collisions at this location were at-angle, also called T-bone, crashes. A signal at this location would not mitigate the potential for T-bone crashes as well as a roundabout and may also result in more rear end crashes.  Because of this, WSDOT will not install a signal at this location.

Isn’t a roundabout a bad idea for a high-speed corridor like SR 503?
WSDOT has had much success around the state with roundabouts on high-speed corridors.  Roundabouts have also been a proven safety countermeasure for decades nationally and statewide.

Here are just a few examples of roundabouts on high-speed corridors in Washington:

• A roundabout was installed at the busy Vancouver intersection of SR 500 and NE 182nd Ave in 2022 where the speed limit is 45 mph.
• Two roundabouts were installed on SR 14 in Washougal in 2019 where the speed limit is 55 mph.
• Three roundabouts were installed near Spokane on Interstate 90 in 2022.
• A roundabout was installed near Spokane at SR 902 and Craig Road in 2019 where the speed limit is 55 mph.
• A two-lane roundabout on US 97 at McDonald/Becker Road in Toppenish was installed in 2021 where the speed limit is 55 mph.

Will freight trucks fit?
Yes! After working with nearby freight companies and tweaking the roundabout design to accommodate their needs, the WSDOT project team included truck-friendly elements like:

• A mountable, flat central island;
• Extra low curbing height; and
• Removable signing.

This project includes a “truck apron,” what is that? 
A truck apron is an intentionally designed element of a roundabout where a raised section of concrete around the center island of the roundabout acts as an extra lane for large vehicles. The back wheels of the oversize vehicle can ride up on the truck apron so the truck can easily complete the turn. The truck apron is raised, and often a different color or material than the roadway, to discourage use by smaller vehicles and emphasize that it is not a normal travel lane.

But there is so much truck traffic!
A neighboring successful example of a roundabout on a high-speed corridor busy with freight traffic would be the SR 500/NE 182^nd Intersection Improvement project where a compact roundabout was installed in 2022. The annual average daily traffic at this location is 11,000 vehicles, with 7% of that traffic being freight traffic. To compare, the annual average daily traffic at SR 503 is 10,500, with 9% being freight traffic.

Why was this intersection prioritized over SR 503 and Gabriel Road?
While there were also a number of collisions at this intersection, the severity of crashes was significantly higher at SR 503 and Rock Creek Road. Also, there have been no fatal or serious injury crashes at Gabriel Road since 2013.

Don’t roundabouts create more congestion?
Contrary to many peoples' perceptions, roundabouts actually move traffic through an intersection more quickly and efficiently, and with less congestion on approaching roads. Roundabouts promote a continuous flow of traffic. Unlike intersections with traffic signals, drivers don’t have to wait for a green light at a roundabout to get through the intersection. Traffic is not required to stop – only yield – so the intersection can handle more traffic in the same amount of time.

Studies by Kansas State University measured traffic flow at intersections before and after conversion to roundabouts. In each case, installing a roundabout led to a 20 percent reduction in delays. Additional studies by the Insurance Institute for Highway Safety (IIHS) of intersections in three states, including Washington, found that roundabouts contributed to an 89 percent reduction in delays and 56 percent reduction in vehicle stops and studies by the Federal Highway Administration (FHWA) show roundabouts can increase traffic capacity by 30 to 50 percent compared to traditional intersections.

Won’t this intersection someday be four lanes?
No, there are currently no plans for this stretch of SR 503 to become four lanes. This roundabout will serve the community for many years to come.

Roundabouts are confusing and will cause more crashes!
WSDOT understands that learning how to move in new traffic patterns can be an adjustment.  However, we have seen time and time again that after a roundabout is constructed, the community quickly learns and becomes more comfortable navigating the roundabout. If you are new to driving through roundabouts, learn how to navigate a roundabout here.

Did WSDOT do public engagement on this project?
Yes! Beginning in 2021, the WSDOT project team has worked with many nearby stakeholders including freight companies, fire districts, property owners and Cowlitz County and Clark County emergency managers and first responders. By working with these critical roadway users, we were able to ensure the roundabout design would accommodate all vehicles that travel through the intersection.

How are you funding this project? 
This roundabout installation project is funded through a portion of the WSDOT Safety Improvement (I2) Program. The goal of this program is to reduce and prevent crashes and each WSDOT region was given resources to address high-priority locations with a roundabout. After a scoring process, SR 503 at Rock Creek Road was identified as the best candidate in the region for the goal of the program.

Are more roundabouts going to be installed in Southwest Washington?
It’s true! Roundabouts are here to stay as a tool in the toolbox to address safety and efficiency, but they may not be the ideal solution for every intersection. Several factors are evaluated when deciding to build a roundabout at a specific intersection. Engineers consider the following characteristics when determining the best solution for a particular intersection:

• Accident history. Data about the number of accidents, type of collision, speeds, and other contributing factors are analyzed.
• Intersection operation. The level of current and projected travel delay being experienced and backups on each leg of the intersection are examined.
• Types of vehicles using the intersection. It is important to look at all of the different kinds of vehicles that use the intersection. This is especially important for intersections frequently used by large trucks, like this one on SR 503.
• Cost. This includes not only the basic costs of construction, but also social and economic costs, right-of-way (buying land) requirements, and long-term maintenance expenses.