Cities often overbuild on parking. Why? Because that's the way it's been done for years -- and because residential developers fear not having enough parking.

But in the state of Washington, the King County Metro Transit agency has been working on a solution to the dilemma -- along with the Center for Neighborhood Technology and the Urban Land Institute Northwest, The Atlantic Cities reported.

For the past year, these entities have tried to measure the factors that dictate residential parking demand in the region, which resulted in the Right Size Parking Calculator web app that estimates parking demand down to a single parcel of land:

Image courtesy of Right Size Parking

How'd they come up with this information? Through a survey of 220 representative multi-family buildings from across the region. Researchers went into each building's lot in the middle of the night to count cars -- because the industry defines peak residential demand as between midnight and 5 a.m.

"On average, we saw what we assumed, which was that parking was overbuilt," Daniel Rowe, a transportation planner with the King County Department of Transportation, told The Atlantic Cities. "Before this project started, we had heard from a lot of different stakeholders in the area that parking was being overbuilt, but we didn’t want to make that assumption. That's the whole reason we did all this data collection – we wanted to verify it."

The buildings were providing about 1.4 parking stalls per housing unit, but residents were only using about 1 stall per unit -- and that oversupply was found across the region.

Pricing information for each building was also evaluated -- for parking and rent, and whether the two costs were bundled. Using that data, as well as data on land use, demographics, job locations and transit, King County Metro Transit, the Center for Neighborhood Technology and the Urban Land Institute Northwest were able to create a model that could estimate parking demand on a given property.

Using the Web app, developers can track how parking demand changes by altering specifications on a particular parcel, such as rent, the square footage and the number of units. The hope? That developers use the tool when planning a project -- and that local governments consider this data in updating their parking regulations, whether that be for more parking or less.

"The name 'Right Size' is very conscious because we don’t want to just say 'in all cases there should be less parking,'" said Ron Posthuma, the assistant director of the King County Department of Transportation. "In some cases, maybe there should be more."