Diverging diamond interchange design won’t meet demands of area traffic | Letter

A diverging diamond intersection may look better, but is no substitute for the traffic-moving ability of ramps and fly-overs.

I am writing to those in the Snoqualmie community and WSDOT design sections responsible for the design and approval of improvements to the I-90/S.R. 18 interchange. The proposed Diverging Diamond Interchange (DDI) concept, I suspect, will eventually be overhwelmed by the traffic demands.

While in the St. Louis, Mo., area this past summer, I traveled through a recently completed DDI on Dorsett Road and I-270. That interchange carries a fraction of the traffic that 90 and 18 carry and during midday, traffic on this interchange were still congested.

I did 30-plus years of service with Washington State in a profession closely linked to transportation and often wondered at the short-sightedness of traffic engineering designs. The original eastbound 520 and 405, and Northbound 405 and 167 interchanges were two good examples. Both clearly illustrate the shortcomings of trying to route crossing traffic on the same plane — it simply doesn’t work.

How Snoqualmie Ridge was developed without corresponding improvements to this interchange leaves one wondering who dropped the ball. It didn’t take clairvoyance to see what lay ahead. Snoqualmie Ridge and North Bend continue to grow, as does the S.R. 18 corridor. Traffic continues to increase and DDIs simply cannot adjust for that increase in volume.

I understand costs as a consideration, but the DDI is a poor substitute for dedicated ramps and flyovers. I would challenge anyone complaining of appearances associated with large concrete interchanges to make an educated decision, a functional highway flyover, or slow-moving traffic slogging its way through a DDI.

John Anderson

Fall City

More in Letters to the Editor

Hope springs from Florida school shooting, in youth movement | Letter

There is a sliver of hope amidst the utter gloom of the… Continue reading

If our leaders won’t change gun laws, it’s time to change our leaders| Letter

I couldn’t sleep last Wednesday. I tossed and turned, the images of… Continue reading

King County wasn’t named for Dr. King, but renamed | Letter

While perusing your website, I came across a headline (Martin Luther King’s… Continue reading

Community support made Snoqualmie Valley Food Bank a reality | Letter

The Board of Directors of the Snoqualmie Valley Food Bank, now celebrating… Continue reading

Give President Trump a chance | Letter

Why is it that when Clinton and Obama said we needed a… Continue reading

Tell legislators we need progressive school funding model | Letter

As the McCleary tax bills are coming out, voters are starting to… Continue reading

Replace Nunes as House Intelligence Committee chairperson | Letter

The actions of House Intelligence Committee chair, Devin Nunes, undoubtedly makes Vladimir… Continue reading

Rossi works with both sides of the aisle; attack on his bipartisanship is laughable | Letter

The attacks on Dino Rossi (“Rossi’s partisan politics don’t belong in Congress,”… Continue reading

Most Read