City staff overruled its own engineer in favor of STCA’s engineer on Town Center traffic impact

By Miki Mullor 

Controversy erupted in August when the City of Sammamish announced that STCA’s Town Center Phase I project passed traffic concurrency. 

The City Council convened for a special meeting Aug. 20 to question how was it that this project, 419 homes and commercial space, that has failed concurrency for nine month suddenly passed it.

Related stories:

Now, emails obtained by the Sammamish Comment through a public records request reveal that city staff inexplicably overruled its own engineer in favor of STCA’s engineer when forecasting the number of car trips the project would generate. 

The staff’s decision lowered the forecasted traffic impact of STCA Phase I by at least 19% in the AM and 30% in the PM peak hours. 

In order to fully understand the implications of ignoring the city traffic engineer and accepting STCA’s traffic consultant data instead, some background is necessary. 

Concurrency changes in the last 18 months

Obtaining a concurrency certificate is an important step in a building permitting process. According to the Growth Management Act (GMA), cities must prohibit development if it causes the level of service of roads to drop below the city’s standards. In lay terms, a level of service means the level of congestion the city is willing to accept before development must stop. 

During the last 18 months, the city council worked on revising the concurrency rules after it was revealed that since 2005 it was set up to “always pass” and allow unchecked development.  

The first attempt took six months and yielded practically the same result because city staff misled City Council to think the new program will account for congestion, only to admit in May 2018 it won’t. 

A second attempt, led by Deputy Mayor Karen Moran, added another layer (Volume over Capacity, or “V/C”) that checked the volume of cars on the city’s arterials. Unlike the first method staff proposed, this method was simpler to understand and less vulnerable to manipulation.

Two arterials, East Lake Sammamish Parkway (ELSP) and Sahalee Way, failed the V/C standard. The city council exempted ELSP from the V/C standard but Sahalee Way remained failing, thus halting development, including STCA Phase I. 

STCA Phase I passes concurrency 

Council Member Pam Stuart

In December, then-Interim City Manager Larry Patterson reported that new development cannot pass the new concurrency system without some improvements to Sahalee Way.  In May, Council Member Pam Stuart moved to exempt the Town Center area from Sahalee V/C to allow it to move forward but couldn’t get a majority vote. Council Members Ramiro Valderrama and Jason Ritchie voted with Stuart. 

Last August, the city council and the public were surprised to learn that STCA Phase I passed the concurrency test.  Mayor Christie Malchow and Deputy Mayor Moran called a Special City Council Meeting Aug. 20 to question staff on how it passed. 

At the next meeting Sept. 5, the council ordered an independent audit of the concurrency test and the traffic forecast model it was based on. 

A traffic forecast model is a computer simulation that simulates how many cars leave each development in the city and where those cars go, and on which roads (known as “car trips”). The forecasted volume on each arterial road is then compared to the city’s level of service standards to see if the development will cause a future concurrency failure.  If it does not, then a certificate concurrency is issued by the city and the development can move to the next step in the permitting process. 

How many cars coming from new homes?

An important step of the concurrency test is a “trip generation memo” in which the developer proposes the number of “car trips” the development will generate in the AM and PM peak hours.  The assumptions in the memo are not arbitrary but normally rooted by some reference data or industry benchmarks based on the type of development. For example, a single family house generates many more  trips than apartments. 

This initial “trip generation” value is important to set the stage for the rest of the test.  The lower it is, the less impact the development will have on the road network, thus more likely to pass concurrency.  

Once submitted, a city traffic engineer will review the developer’s assumptions in the “traffic generation memo” and will either accept or require changes. 

City’s engineer recommended a conservative approach 

Josh Anderson, DEA

Josh Anderson, from David Evans Associates (“DEA”), is a contract traffic engineer for the city and was assigned to review STCA’s trip generation model. 

In a March 7 memo, Anderson writes:

“After a detailed review, DEA staff want to draw attention to the following assumptions. These assumptions have a large impact on the total trip generation for the proposed Town Center (TC) and while not specifically incorrect, could be adjusted to result in a more conservative trip generation estimate.”

Specifically, Anderson calls out the trip generation factors used by the developer, 0.36 and 0.44 per unit, for the AM and PM peak hours, respectively.  Anderson explains:

“ITE LUC 221 shows a trip generation rate of 0.36 and 0.44 trips per unit for the AM and PM peak hours, respectively.” 

Sammamish’s calibrated travel demand model uses multi-family trip generation rates of 0.44 and 0.62 trips per unit for the AM and PM peak hours.” 

Josh Anderson, David Evans and Associates

ITE LUC 221 is a factor defined in a generalized industry manual published by the Institute of Transportation Engineers (ITE). The “calibrated model” is a traffic forecast model that has been matched to Sammamish’s specific circumstances. 

Anderson’s recommendation to match the test parameters to those used by Sammamish’s specific model would have increased the forecasted traffic from STCA’s project by 22% in the AM and 40% in the AM peak hours. 

City staff overrules Anderson, its own engineer 

But, when Isabel Diaz, the city staff member who sent Anderson’s memo back to STCA, it showed that staff already overruled Anderson’s recommendation, before even showing it to STCA:

“Please find attached Trip Generation Memo review conducted by David Evans and Associates (DEA) for Sammamish Town Center (STC) Phase I. We are okay with the assumption on ITE land use code that was used for multi-family (LUC 221) in your memo,” accepting STCA’s position over Anderson’s recommendation.

Staff email to STCA, overruling their own engineer

Indeed, in a Mar. 22 memo sent back to the City, STCA’s engineer acknowledged staff’s decision to overrule Anderson:

“Based on Isabel Diaz’s e-mail to me dated March 8, 2019, we understand Sammamish staff is agreeable to using average trip generation rates for ITE Land Use Code 221 (“Multifamily Housing (Mid-Rise)”) to estimate vehicle trip generation for transportation concurrency testing purposes.” 

STCA’s engineer’s acknowledgment of staff overruling Anderson

City administration evades tough questions 

The Comment asked the city who made the decision to overrule Anderson in favor of STCA.  Sharon Gavin, Communication Manager for the city sidestepped the question:

“Determining the completeness of a Traffic Concurrency Review Application (TCR) is a consensus,  administrative decision between the Departments of Community Development (DCD) and Public Works (PW).” 

Sharon Gavin, Communications Manager, City of Sammamish

Gavin did not answer the question who specifically authorized Diaz to overrule Anderson.  The authority for issuing concurrency certificates lies with Cheryl Paston, acting Director of Public Works. Paston was copied on Diaz’ email. 

The Comment further asked why was the developer’s position taken over a city engineer’s recommendation, to which Gavin said:

“After reviewing the TCR application with DCD, Public Works informed STCA that the City had accepted the Land Use Code LUC 221 for the multifamily portion of their project since it was consistent with the most current ITE Trip Generation Manual, which is required by the City’s code per 14A.05.010” 

Sharon Gavin, Communications Manager, City of Sammamish

Again, Gavin did not explain why Anderson’s recommendation was overruled. In his recommendation, Anderson acknowledged STCA’s position may be generally correct but does not match Sammamish calibrated traffic model.

When reached for comments, Council Member Tom Hornish referred to the following comments he made during the Sept. 5 city council meeting: 

“I would posit that instead of taking the developer side and being concerned about the developer suing us, we take the position of the citizens and let the developer sue us instead of the citizens have to… If it’s a gray area, don’t default just to take the developer’s side.”

Council Member Tom Hornish

References :

Get real time updates to your email when news are posted. Your email will not be shared with third parties

Join 1,818 other subscribers

Copyright (c) 2022 The Sammamish Comment

6 thoughts on “City staff overruled its own engineer in favor of STCA’s engineer on Town Center traffic impact

  1. “Scientists errors don’t come from bad math, but bad assumptions.” Also true about city staff, study designers and cities.

    Assumptions, models and studies can be hooey and bad decisions made as a consequence that do a lot of harm.

    Molly Ciliberti

    Made plenty of stupid assumptions myself

    You can’t roller skate in a buffalo herd, but you can be happy if you put your mind to it.


  2. I guess it’s a good thing the city isn’t in the weather forecasting business. At least they’re able to find another bit of science that can be sacrificed for the “public good” (snort). Our tax dollars at work!

  3. Thanks Miki for once again shining a light on the developers shills and stooges. Watch the cockroaches scurry. Maybe it’s time to stomp a few of the big ones.

Leave a Reply

Please log in using one of these methods to post your comment: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s