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SR 524 - Locust & Larch Way - Intersection Improvements - Alternatives considered

WSDOT looked at six different options when analyzing the Locust Way and Larch Way intersections on SR 524 to reduce congestion-related collisions. In studying the options, engineers also reviewed whether each would improve or negatively affect congestion over a ten-year period.

This photo also shows the location constraints the intersection improvement project must work within. Martha Creek and its stream buffer is on the south side of SR 524 while Swamp Creek runs north-south and crosses under Magnolia Road and the SR 524 Swamp Creek bridge. Certain regulations must be followed to avoid negative impacts to the streams and buffer zones.

The two streams and stream buffers along SR 524 at Locust Way and Larch Way.

Option 1 - Do nothing.

  • If no improvement work occurred, collisions would likely continue to increase as more drivers use the road, stopping to make left turns and taking more risks to turn left in the gaps of oncoming traffic. This option is not recommended.

Option 2 - Add left turns without a traffic signal.

  • This would require widening SR 524 and addressing the constraints of Swamp Creek, Martha Creek, the stream buffers, the Swamp Creek bridge and the I-405 bridge columns. There is no funding available for the widening, right of way and environmental issues that need to be addressed.
  • Headed eastbound, the amount of distance needed for a left turn lane onto Magnolia Road would encroach on the Swamp Creek bridge. In addition, the distance needed for an eastbound left turn lane onto Larch Way for afternoon traffic would overlap and interfere with a westbound left turn lane that's needed for morning traffic turning left onto Locust Way. 
  • This option is not recommended due to limited funding and roadway space constraints. 

Option 3 - Add left turns, plus a right turn lane at Larch Way, without a traffic signal.

  • The drawbacks are identical to those listed in option 2, but even more room would be needed to add westbound right turn lane at Larch Way. 
  • This option is not recommended due to limited funding.

Option 4 - Add traffic signals, but no turn lanes.

  • This option looked at adding traffic signals at the intersections, allowing one direction at a time to move through each intersection. For example, eastbound traffic would get a green, while all other intersections have red until their turn came. This would essentially turn SR 524 and the side streets into roads where only one direction is moving at a time.
  • This option is not recommended due to limited funding and negative traffic effects.

Option 5 - Add left turn lanes with traffic signals.

  • This would require widening SR 524 and addressing the constraints of Swamp Creek, Martha Creek, the Swamp Creek bridge, stream buffers and the I-405 bridge columns. There is no funding available for the widening, right of way and environmental issues that need to be addressed.
  • Traffic modeling also showed that within ten years traffic on Larch Way trying to reach SR 524 in the morning would likely experience backups more than three football fields long due to growth in the area. The higher volume of traffic on SR 524 would have longer periods of a green light. We would not be able to provide enough green light time to the drivers on Larch Way to completely clear it. The line of cars waiting for the light would simply continue to grow. Initially, collisions might be reduced, but the operational drawbacks would be severe by 2028. 
  • This option is not recommended due to limited funding and the additional traffic backups that would occur.

Option 6 - Roundabouts

  • This alternative achieved the best operation for traffic along with a proven record of reducing collisions.
  • This option is recommended due to the improvements in safety, positive traffic effects and the ability to design and build the project within the current funding.