We’re referring to the study for Green Lake Mixed Use, 419 NE 71ST St. We wrote about the report that was done, noting that it was impossible, based on the information provided in that document, to determine how specific results had been derived. Despite this, Seattle Department of Construction & Inspections (Seattle DCI, previously, Seattle DPD) still approved it.
It’s important to scrutinize developer-funded traffic studies, because too often questionable results are rubber-stamped by the city without proper due diligence, at the expense of the local community. 419 is also of interest, even though it’s already under construction, because a cumulative parking analysis required for a project still undergoing review, 417 NE 73rd St, should have included spillover parking from 419.
We dug into the study done for 419, including sending inquiries to Transportation Engineering NorthWest (TENW), the firm that prepared it for the developer. TENW answered enough questions so that we could reconstruct their analysis. However, the firm did not respond to a question about the source of a key claim regarding the impact of the Roosevelt light rail station (LRT) on vehicle ownership by 419’s residents. John Shaw, the Seattle DCI transportation reviewer for the project—and many other projects in the east Green Lake community including 417—also did not respond to email inquiries regarding the LRT claim or how TENW derived results in its analysis. As we noted above, it would have been impossible for Shaw to answer these questions based solely on TENW’s report.
419 will be a mixed-used project, with 130 residential units, 106 parking stalls, and over 14,500 SF of retail space that will be occupied by Bartell Drugs.
According to the parking analysis performed by TENW, the peak parking demand for the project from residential and retail users will be 99 vehicles. As a result, the firm concludes, “no on-street parking demand impacts are expected.”
Let’s assess how accurate that claim is. Here are TENW’s steps:
First, it plugged 419’s residential and retail sizes and land use codes into tables from ITE Parking Generation, 4th Edition, to conclude that the project’s peak weekday residential and retail parking demand would be 120 and 37 stalls, respectively. You can have endless debates about the approach TENW took (including the fact that two-thirds of the project samples in the ITE table had vehicles per dwelling unit numbers that exceeded the .92 figure TENW used), but we’ll defer other than to adjust the 120 to 124 because of an error in TENW’s math.1
Next, TENW used the proximity of the project to the future Roosevelt light rail station to reduce residential vehicle ownership for 419 by another 20 percent, from 120 to 96.2 TENW provides no support for this argument, only citing the existence of Sound Transit documents. However, as we noted previously, neither TENW nor DCI’s John Shaw, who approved TENW’s analysis, responded to requests for this documentation. Because of this, we’ve issued public-record requests to both Sound Transit and Seattle DCI for relevant documents.
We’ve also researched US Census tables regarding vehicle ownership rates for rental housing units near Seattle light rail stations similar to Roosevelt and found nothing in that data that would support TENW’s claim.
The Roosevelt LRT won’t be built until 2021, five years from now. That alone should remove it from consideration in any calculations involving traffic impacts for projects being built today. Nonetheless, until TENW or Seattle DCI can provide credible sources for the LRT reduction, it should not factor into the parking analysis. Claims that are fundamental to the outcome of a report provided to the public should be fully sourced.
The third step in TENW’s parking analysis used 2010 US Census data for vehicle ownership for rental housing units in the census tract 419 sits in, tract 36.3 This data shows that 21% of the units in the tract didn’t have cars. For the Seattle metro area, this number was 8%. TENW split the difference between the two and reduced the residential vehicle ownership result of step #2 by 13 percent, i.e., from 96 to 83. They kept their estimate of 37 for the peak weekday retail parking demand.
TENW’s use of Census data here is on shaky ground for multiple reasons, including the fact that the ITE tables in step #1, which use statistical data collected from existing projects, already have demographics baked in, and so there’s no basis for whittling results down in an additional step using census data. Nonetheless, we’ll use TENW’s numbers in our analysis.
In the final step of its analysis, TENW adjusted its numbers to account for the fact that peak residential parking demand occurs during the evening hours, when people are home from work, etc. Peak retail parking, on the other hand, typically occurs during the daytime. For the adjustment, TENW used data from Shared Parking, 2nd Edition, which shows that residential parking demand is 25 to 35 percent lower in the daytime from its evening peak. Using the 25 percent figure, TENW reduced the residential parking demand estimate of step #3 to 62 (.75*83) for daytime hours. Combining this with the peak retail parking demand of 37, TENW concluded that the peak parking demand for 419 will be 99 (62+37).
The problem with this approach is it’s a crude application of Shared Parking, which provides hourly parking demand rates for shoppers and residents. According to these rates, there are hours in the late afternoon and early evening when the combined parking demand of these two groups is far in excess of TENW’s estimates. For example, according to Shared Parking, residential parking demand at 6 PM is 90% of its peak. Just an hour later, this number rises to 97%. Meanwhile, retail parking demand during these hours has barely slipped from its high earlier in the day.
We performed an analysis of 419’s weekday parking demand, making adjustments based on the observations above, but otherwise using the identical approach taken by TENW. The adjustments include:
- In Step #1, TENW’s peak weekday residential estimate of 120 was revised to 124
- In Step #2, TENW’s reduction due to 419’s proximity to the Roosevelt light rail station was removed from the analysis altogether
- In Step #4, time-of-day factors for each hour from Shared Parking, 2nd Edition were applied rather than TENW’s single number
We’ve summarized our results here. For comparison, we’ve also included estimates using the King County Right Size Parking Calculator, which TENW used to measure parking demand just six months before at a nearby project, Crosby Greenlake at 414 NE Ravenna Boulevard. The data for the calculator was based on a careful analysis of 419’s apartment characteristics and rental fees for units at Crosby Greenlake and Green Lake Village.
Here are some key takeaways from our analysis:
- Until the light rail station at Roosevelt is completed in 2021, analysis based on TENW’s own methods shows that weekday spillover parking from 419 will be substantial, averaging 26 vehicles from 5 to 9 pm. The spillover does not include parking for Bartell Drugs employees or guests of 419 residents.
- The claim that the spillover will disappear after 2021 depends on the viability of documentation that thus far Seattle DCI has not made available to the public despite multiple requests.
- A parking utilization study TENW did for Crosby Greenlake five months before their parking study for 419, showed that parking demand in the area would exceed 100% legal parking capacity once Crosby was completed and filled.
Regarding the third item, TENW would have had to perform a parking utilization study for 419 in addition to the one it had already done for the Crosby Greenlake if the firm had determined 419 would have spillover parking.
1 According to the parking statistics collected for land use code 221, Low/Mid-Rise Apartment, Weekday, Urban, the average peak parking demand is 1.2 vehicles per residential unit, or 156 vehicles for 419, which will have 130 units. However, rather than use 1.2, TENW used the smaller .92 that appears as the slope in the least squares fit for the statistical data, P = .92*X + 4, where X is the number of residential units. TENW omitted the 4 in the equation, and the correct result using this approach should have been 124 = .92*130 + 4, not 120 = .92*130.
2 No other project in the vicinity of Roosevelt LRT that is either under review or that has been approved that we surveyed has used this technique to reduce parking impact.
3 Examples include apartments units, a room within a house, or even an entire house.