Background

With a grant from the Federal Highway Administration’s Value Pricing Program, King County Metro Transit assembled information about multi-family residential parking use at more than 200 developments in King County over the winter and spring of 2012; with data from an additional 75 buildings added in 2017. Parking utilization was recorded on Tuesdays, Wednesdays, and Thursdays between midnight and 5 a.m. in all residential spaces identified by property managers in each multi-family development studied. Most of these spaces were on-site, although some property managers identified additional off-site parking areas provided for residents.

The Model

Metro then developed a statistical model to estimate parking use based on building and environmental characteristics. The model was built using regression analysis. The dependent variable was observed vehicles per occupied residential unit (or parking/unit ratio) gathered from the field data. Independent variables are:

• Average Unit's Square Ft.
• Average Occupied Bedroom Count
• Average Unit's Rent^*
• Parking Price per Month^*
• Parking Stalls Provided per Housing Unit
• Percent of Units Designated Affordable
• Gravity measure of Employment
• Gravity measure of Population
• Gravity measure of Transit Service

Taken together, these variables form a strong model for predicting the parking/unit. A resulting R-square value of 0.85 indicates that 85 percent of the variation observed in parking use can be explained through these nine variables.

^* A factor of 1.07117 was applied to the 2011-2012 data to account for inflation and transform into 2017 dollars.