The intersection design’s primary goal is balance: balancing the precious space between drivers coming from or going to Simonds Road, 100th Avenue Northeast, or Northeast 145th Street. And in a broader sense, it is also attempting to balance the City’s transportation goals and its environmental obligations.
Those environmental obligations are most specifically defined by a federal requirement to limit the space allotted to a ‘pollution-generating surface’ and to retain—as much as is practicable—the areas of a street that do not generate pollution.
The pollution-generating surface on 100th Avenue Northeast is every surface that vehicles touch and that convey the residue they leave behind—heavy metals from the exhaust, oil, gasoline, and, most lethally tire fragments.
Rain mixes with these pollutants and carries them into storm drains, which, drain into salmon-bearing streams before dumping into Lake Washington. Researchers have long suspected a chemical in those tire fragments have been quietly and efficiently killing Coho salmon in urban streams.
And in 2020, University of Washington researchers identified it. That discovery highlighted the importance of ensuring that street improvements maximize as much as is practicable the amount of space that does not generate pollution.
One good strategy to maximize ‘non-pollution generating space’ is to build an elevated median and plant pollutant-filtering trees in it. However, if the analysis had determined the space now occupied by the median would be necessary for the intersection’s ability to efficiently convey traffic through it, the project’s design team would have instead used that space for vehicles and found other ways of reducing pollution-generating space.
Analysis showed,(PDF, 1MB) however, that an extra full lane there is just not necessary. Here’s why: The through-lane between the Simonds Road intersection and Northeast 145th Street would never have to accommodate more than one lane of traffic at a time.
That’s because the traffic signal at Simonds Road—which the project upgraded and more efficiently coordinated with the traffic signal at Northeast 145th Street—will never allow both northbound lanes of traffic through the Simonds Road intersection at the same time.
As such, Kirkland’s traffic engineers believe the line of automobiles queued at a red light at Northeast 145th Street would rarely, if ever, extend so far to the south that it would block automobiles from entering the right-turning lane onto Northeast 145th Street. And just to be sure, they extended the right-turn-lane a few hundred feet to the south.