Density Meets Undesirability

Analyzing the Location of Multi-Family Housing in Seattle

Overview

The United States is currently experiencing a housing crisis. Nationwide, 31.5% of households are cost-burdened, meaning they spend over 30% of their income on housing (JCHS, 2019). The city of Seattle, Washington is no different, with around a third of its residents being cost-burdened. In order to meet housing demand, it is estimated that King County, where Seattle is located, will need to construct 17,000 housing units every year for the next 20 years (“WA needs”, 2023).

Seattle's Single-Family and Multi-Family Housing

Looking at the city’s current land use, single-family housing accounts for 29.4 square miles, while multi-family housing only takes up one sixth of that. Despite this, rentals make up the majority of housing units in the city (“About Seattle”, n.d.). The fact that multi-family housing takes up such a small portion of the land, relevant to the amount of housing provided, sparked this investigation into the conditions present near multi-family housing.

Research Questions:

  • Is existing multi-family housing located in areas of Seattle with potentially higher levels of air pollution?
  • Do neighborhoods with higher concentration of multi-family housing also have higher concentrations of pedestrian and cyclist collisions?

Air Pollution

Air pollution is one major factor that will be investigated. Seattle’s Department of Construction & Inspections regards highways & major arterial roads with high levels of diesel truck traffic as the largest sources of air pollution (2015). These sources are found throughout the city, with the most dramatic example being interstate 5, which runs north-south through the center of the city as well as many other population centers in the city. Other sources include diesel locomotives on railway lines, as well as diesel engines for marine and port uses. This air pollution can cause increased risk of cancer (Seattle Department of Construction & Inspections, 2015).

One aspect of this is arterial streets. These streets were identified by selecting all roads classified as "Interstate/Freeway", "Principal Arterial", or "County Arterial". Next, a 200 meter buffer zone was created around these arterials, based on information provided in Seattle's Comprehensive Plan (Seattle Department of Construction & Inspections, 2015).

The other aspect, freight railways, includes all active railroads in the city which run diesel locomotives. A 187-meter buffer zone was chosen based off of the US EPA’s Rail Facility Best Practices to Improve Air Quality.

Arterial Roads and Freight Railways

Single-Family and Multi-Family Housing near arterial roads and freight railways.

64.7% of Seattle's multi-family 27.2% of Seattle's single-family

Ranking of Seattle's Neighborhoods

While most of Seattle's multi-family housing is located within these air pollution zones, a further analysis was conducted to determine the proximity of multi-family housing to arterial roads and freight railways in each of Seattle's neighborhoods.

Every neighborhood was given a score based on (1) its total amount of multi-family housing and (2) the percentage of multi-family housing which is located within the air pollution buffer zone. In the calculation, the amount of housing had a weight of 1 and the percentage of polluted housing had a weight of 3.

Using our calculations:

  • A high-scoring neighborhood = high amount of multi-family housing, with little to none of it located within pollution areas.
  • A low-scoring neighborhood = very little multi-family housing, with most to all of it located within pollution areas.

Here are the results:

1

Alki (Best)

  • 2374 Multi-Family Units
  • 0% in Pollution Zone

2

Lawson Park (2nd Best)

  • 2362 Multi-Family Units
  • 23.03% in Pollution Zone
3

Genesee (3rd Best)

  • 1249 Multi-Family Units
  • 10.73% in Pollution Zone
4

Laurelhurst (Worst)

  • 233 Multi-Family Units
  • 100% in Pollution Zone
5

Portage Bay (2nd Worst)

  • 182 Multi-Family Units
  • 96.7% in Pollution Zone
6

Westlake (3rd Worst)

  • 640 Multi-Family Units
  • 100% in Pollution Zone

Pedestrian and Cyclist Safety

Many parts of Seattle containing high amounts of multi-family housing have zero parking requirements and high proximity to public transit, leading to a high concentration of pedestrians in these areas (“Multifamily Residential”, 2011). With this in mind, the question of whether or not multi-family housing is disproportionately located in areas with higher rates of pedestrian/cyclist collisions was investigated. Different roads affect different aspects of pedestrian access and safety in Seattle. While interstate highways act as barriers for pedestrian access, high-trafficked state highways, though they do not cut off pedestrian access, can be extremely dangerous for pedestrians. In 2022, “93% of pedestrian deaths in Seattle happened on long, straight, wide roads - arterial streets” (Board, 2023).

Using a kernel density analysis, the areas with the highest concentration of pedestrian and cyclist collisions between 2013-2023 were identified.


Analysis of Neighborhoods

In order to analyze whether there is a correlation between multi-family housing and areas with high amounts of pedestrian and cyclist collisions, the city was analyzed at a neighborhood-scale.

All 93 neighborhoods ranked

Seattle's neighborhoods were ranked by the total amount pedestrian and cyclist collisions in the year 2023



Ten Neighborhoods with the most collisions

  1. Central Business District (most collisions)
  2. Broadway
  3. University District
  4. Pioneer Square
  5. Belltown
  6. First Hill
  7. South Lake Union
  8. SODO
  9. Denny Triangle
  10. Wallingford

These 10 neighborhoods account for over 38% of the pedestrian and cyclist collisions in the city



Single-Family and Multi-Family Housing in these neighborhoods

Housing Units

  • Multi-Family: 38,371 units (88.1%)
  • Single-Family: 5,167 units (11.9%)


Multi-Family Housing Percentage vs. Pedestrian & Cyclist Collisions per mi 2 

This scatterplot shows that neighborhoods with a high percentage of multi-family housing are extremely likely to also be neighborhoods with a high amount of pedestrian and cyclist collisions per square mile. All neighborhoods with 90% of their housing being multi-family housing have a higher concentration of collisions than the neighborhoods with less than 90% multi-family housing. Of those neighborhoods with over 90%, Lower Queen Anne and Eastlake have the lowest concentration of collisions. The Central Business District is by far the neighborhood with the highest concentration of collisions. Sand Point, a neighborhood with zero multifamily housing, has a relatively low number of collisions per square mile.


Conclusions

Looking at the data analyzed in this report, it can be concluded that multi-family housing in the city of Seattle is disproportionately located near sources of air pollution, as well as areas with high concentrations of pedestrian and cyclist collisions.

It must be noted that the cause of these conditions cannot be determined from the data presented here. Further research must be completed in order to better understand the relationship between multi-family housing, air pollution, and pedestrian/cyclist safety.


Bibliography

About Seattle. (n.d.).  Office of Planning and Community Development; City of Seattle. https://www.seattle.gov/opcd/population-and-demographics/about-seattle#landuse

Board, C. (2023). Traffic Deaths Increased Over Past Several Years in Seattle. King 5 News. https://www.king5.com/article/news/local/seattle/sdot-vision-zero-deaths-increase/281-1b16f724-5caa-4afc-a1b8-e347504af920

JCHS. (2019). State of the Nation’s Housing 2019. Joint Center for Housing Studies at Harvard University. https://www.jchs.harvard.edu/sites/default/files/Harvard_JCHS_State_of_the_ Nations_Housing_2019.pdfNotes 

Multifamily Residential Parking Policy Best Practices. (2011). King County Metro Transit. https://metro.kingcounty.gov/up/projects/right-size-parking/pdf/rsp-parking-policy-menu-v7.pdf

Rail Facility Best Practices to Improve Air Quality. US EPA. (n.d.). https://www.epa.gov/ports-initiative/rail-facility-best-practices-improve-air-quality

Seattle Department of Construction & Inspections. (2015). Seattle Comprehensive Plan Update (Section 3.2 - Air Quality and Greenhouse Gas Emissions). https://www.seattle.gov/documents/Departments/OPCD/OngoingInitiatives/SeattlesComprehensivePlan/3-2AirQualityampGHGDEIS.pdf

WA Needs More than 1 million New Homes Over Next 20 Years. (2023). The Seattle Times. https://www.seattletimes.com/business/real-estate/king-co-needs-17k-new-homes-every-year-to-address-housing-shortage/ 

64.7% of Seattle's multi-family 27.2% of Seattle's single-family