Scenario 1: No Action
Existing Lane Configuration and Traffic Patterns
Commercial Avenue and 12th Street is a major intersection for motor vehicles travelling into and out of downtown Anacortes as well as to and from the Washington State Ferry Terminal. The existing intersection has traffic signals on all four legs of the intersection. Commercial Avenue has five lanes of traffic in each direction, each with two through lanes and a center turn lane. 12th Street west of Commercial Avenue has three lanes of traffic, one lane westbound towards the Washington State Ferry Terminal and two lanes eastbound. 12th Street east of Commercial Avenue is a driveway for a Safeway grocery store. Aside from this driveway, the posted speed limit for Commercial Avenue and 12th Street is 30 mph through this intersection.
The most common motor vehicle turning movements at the intersection are people headed towards and away from the Washington State Ferry terminal. More specifically, this includes people making a left turn from Commercial Avenue onto 12th Street and people turning right from 12th Street onto Commercial Avenue. Another major traffic movement is through the intersection along Commercial Avenue into and out of downtown Anacortes.
Bicycle and Pedestrian Conditions
The current conditions at the intersection are limiting for bicycle and pedestrian travel. For pedestrians, striped crosswalks and pedestrian signals only exist on three legs of the intersection. The southern leg of the intersection across Commercial Avenue does not allow for pedestrians to cross. The crosswalk on the eastern leg of the intersection across the Safeway driveway has also been worn down and is barely visible. Additionally, the sidewalks are relatively narrow, most of the curb ramps are in poor condition and do not line up with the crosswalks, and the crossing distances are very long. Lastly, no bicycle facilities exist approaching or through the intersection.
Opportunities and Challenges with Current Design
The current intersection conditions present a number of challenges and opportunities. The existing conditions for pedestrians mentioned above make it difficult for people to safely and comfortably cross the street, particularly for the most vulnerable road users such as children, the elderly, and people with disabilities. People on bicycles have no option but to share the road with motor vehicles, which is particularly dangerous on these arterial roadways with high traffic volumes and speeds.
For people walking and biking, the existing intersection design is particularly dangerous when motor vehicles turn left from Commercial Avenue onto 12th Street. Left turns, according to a recent study by the Insurance Institute for Highway Safety, account for nearly one third of all pedestrian-involved crashes in the United States. This left turn from Commercial Avenue onto 12th Street is the most common motor vehicle movement through the intersection. Motor vehicles making this turn during peak traffic periods typically queue up all the way south into the 13th Street intersection. Eager drivers striving to make the light at this left turn combined with long pedestrian crossing distances create potentially dangerous situations for pedestrians.
In terms of traffic flow, Level of Service is anticipated to get worse at the northbound left turn going from Commercial Avenue onto 12th Street. Under the current conditions, freight traffic also has limited space to make the eastbound right turn from 12th Street onto Commercial Avenue and the northbound left turn from Commercial Avenue onto 12th Street.
The potential benefits of keeping the existing intersection design include lower costs, no right-of-way acquisition required, and maintaining consistent expectations for traffic patterns including the same overall traffic flow.
|Performance Measure||No Action|
|Bicycle / Pedestrian Conditions||No effect|
|Traffic Flow (Level of Service)||No effect overall; reduced LOS for northbound left turn|
|Vehicle Capacity||No effect|
|Vehicle Queuing||No effect|
Scenario 2: Traditional Intersection
The proposed traditional intersection for Commercial Avenue and 12th Street keeps the same overall traffic patterns but reduces the number of lanes and expands bicycle and pedestrian space. Commercial Avenue is reduced from five lanes to three lanes–one through lane in each direction with a center turn lane. The approach to the intersection from the Safeway driveway is also reduced from three lanes to two lanes–one lane in each direction. 12th Street west of Commercial Avenue keeps the number of motor vehicle travel lanes. In addition to the reduced number of motor vehicle travel lanes, bicycle lanes and curb extensions are included as well as enhanced traffic signal timing. Finally, a striped crosswalk and pedestrian signal are added on the south leg of the intersection across Commercial Avenue.
Opportunities and Challenges
These improvements reduce bicycle and pedestrian crossing distances, enhance visibility for all users, and reduce bicycle and pedestrian exposure to motor vehicle traffic. Pedestrians are also now able to cross all four legs of the intersection. Additionally, a reduced number of motor vehicle travel lanes has been shown to slow motor vehicle speeds. Overall, these improvements should reduce the likelihood and severity of motor vehicle collisions.
In addition to the many safety benefits associated with the traditional intersection, some of the challenges to this proposed design include a potential increase in rear-end crashes, reduced level of service and capacity for the northbound left turn lane on Commercial Avenue, and reduced capacity for the southbound through-right turn lane on Commercial Avenue.
|Performance Measure||Traditional Intersection|
|Safety||Potential increase in rear-end crashes; Improved bicycle/pedestrian safety|
|Bicycle / Pedestrian Conditions||Shortened crossings; marked crossings; curb extensions; bike lanes|
|Traffic Flow (Level of Service)||No effect overall; reduced LOS for NB left turn|
|Vehicle Capacity||Reduced capacity for NB left turn and SB thru-right turn|
|Vehicle Queuing||Increased queuing for NB left turn|
Scenario 3: Single Lane Roundabout
The third alternative proposal for Commercial Avenue and 12th Street is to replace the existing signalized intersection with a single lane roundabout. Motor vehicles slow down as they approach the roundabout and yield to traffic moving from the left, yielding first to people walking and biking and then to other motor vehicles. As motor vehicles exit the roundabout, they put their right turn signal on and yield again to people walking and biking before moving through the intersection.
This single lane roundabout design includes one lane of motor vehicle traffic and completely separated and slightly raised bicycle lanes and wide sidewalks. Striped crossings for people walking and biking are provided on all four legs of the intersection. The crossing distance on each leg of the intersection also includes median refuges.
Opportunities and Challenges
This single lane roundabout design, with separation and dedicated space for all modes of travel, has been proven to greatly reduce the likelihood and severity of collisions, including a 75 percent reduction in collisions resulting in injury and a 90 percent reduction in collisions resulting in fatalities. The roundabout increases safety by reducing motor vehicle speeds from at least 30mph, which is the current speed limit, down to between 15 and 20mph. Single lane roundabouts also reduce the number of potential conflict points, or exposure, between people driving, biking, and walking. Lastly, the roundabout would also reduce crossing distances for people walking and biking and increase visibility between all modes of traffic.
In addition to increased safety, the proposed single lane roundabout is expected to increase traffic flow and capacity and reduce motor vehicle queuing for turns. The roundabout, in contrast to the traditional intersection, is also designed to accommodate freight traffic through a mountable center island.
Lastly, the roundabout design, because of the large center island, has the most potential to create a sense of place and beautify the intersection through features like public art and greenery.
Some of the challenges to the single lane roundabout design might be added cost, right-of-way acquisition, and slightly less direct travel patterns, especially for people walking.
|Performance Measure||Single Lane Roundabout|
|Safety||Improved safety for all users|
|Bicycle / Pedestrian Conditions||Separated bicycle lanes; widened sidewalks; shortened crossings; minimized conflict points; slower speeds|
|Traffic Flow (Level of Service)||Increased overall|
|Vehicle Capacity||Increased capacity|
|Vehicle Queuing||Reduced queuing|
|Performance Measure||No Action||Traditional Intersection||Single Lane Roundabout|
|Safety||No effect||Potential increase in rear-end crashes; Improved bicycle/pedestrian safety||Improved safety for all users|
|Bicycle / Pedestrian Conditions||No effect (poor current conditions)||Shortened crossings; marked crossings; curb extensions; bike lanes||Separated bicycle lanes; widened sidewalks; shortened crossings; minimized conflict points; slower speeds|
|Traffic Flow (LOS)||No effect overall; reduced LOS for NB* left turn||No effect overall; reduced LOS for NB* left turn||Increased overall|
|Vehicle Capacity||No effect||Reduced capacity for NB* left turn and SB* thru-right turn||Increased capacity|
|Vehicle Queuing||No effect||Increased queuing for NB* left turn||Reduced queuing|
|Freight||No effect (poor current conditions)||No effect||Increased movement|