Transit-oriented development (TOD) has become a standard model for development. Wikipedia defines it as:
a type of urban development that maximizes the amount of residential, business and leisure space within walking distance of public transport. It promotes a symbiotic relationship between dense, compact urban form and public transport use. In doing so, TOD aims to increase public transport ridership by reducing the use of private cars and by promoting sustainable urban growth.
A TOD typically includes a central transit stop (such as a train station, or light rail or bus stop) surrounded by a high-density mixed-use area, with lower-density areas spreading out from this center. A TOD is also typically designed to be more walkable than other built-up areas, through using smaller block sizes and reducing the land area dedicated to automobiles.
Transit-oriented development is an important part of reducing greenhouse gas emissions because people who live in denser, more urban areas tend to have a smaller carbon footprint. This is because in cities jobs, housing, and services are closely colocated, so people in cities do not need to travel as far. When they do travel, they have more alternatives to automobile use, and are more likely to use public transit, walking and cycling instead. Also, in cities people tend to have less space, and therefore they have smaller homes, leading to lower emissions from heating and cooling. This is illustrated by a map of US Household Carbon Footprint by zip code included in this paper by Christopher Jones and Daniel M. Kammen that was published in Nature: Spatial Distribution of U.S. Household Carbon Footprints Reveals Suburbanization Undermines Greenhouse Gas Benefits of Urban Population Density:
Seattle adopted transit-oriented development in the early 90's by designating core areas in certain neighborhoods as urban centers or urban villages. Downtown, First Hill, the University District and Northgate were designated regionally and in Seattle's Comprehensive Plan as major urban growth centers. They include high density commercial and residential development and are high priority for service by light rail,
Urban villages are generally zoned neighborhood commercial or low to mid- rise residential; they encourage moderate density and are prioritized for more frequent transit service.
In the context of regional growth management planning, increased growth in urban centers and villages was also a central strategy in the effort to reduce development outside the urban core, in order to preserve forests and farmland. This was part of the King County's response to Washington's passage of the Growth Management Act. The intention of policymakers was that there would be plenty of housing for everyone, but it would be concentrated in urban areas where people would have reduced travel to jobs, schools, and services while still being able to go outside the city to enjoy the natural bounty that makes the region such a special place to live.
Seattle has added on to its urban villages over time, and the population has grown significantly since the urban village concept was initiated. We've grown by 25% just in the last 10 years. To the right is a map of Seattle's urban centers and villages. They make up 18% of the land area that permits residential development in the city, but in 2017 they accounted for 88% of the housing growth.
Still today compared to most peer cities with expensive housing, Seattle devotes more of its land area to single-family homes.
Recent Zoning Changes
Mandatory Housing Affordability
In spring of 2019, Seattle adopted Mandatory Housing Affordability (MHA) that requires new development in core zones to either include affordable homes, or contribute to a City fund for affordable housing.
Backyard Cottages and Basement Units
In the summer of 2019, Seattle voted to allow detached accessory dwelling units (cottages or DADUs), and attached accessory dwelling units (basement units or AADUs) to provide more housing options. Backyard cottages and basement units can now be added to most lots in single family zoned areas. This allows for more housing in single family zones, but the impact is relatively modest: the Environmental Impact Statement projects 2300 units built over 10 years.
New Comprehensive Plan
Seattle is beginning work this fall on a new Comprehensive Plan, which will update Urban Growth Zones, and incorporate changes in zoning and associated changes in services, parks, schools, transit. One big question is how it will accommodate new growth; will it continue the policy of keeping most of Seattle's residential land zoned as single family or will it allow multi-family buildings? Portland recently completed a rezone which allows 4-unit apartment buildings in all previously single family zones, or up to 6 units if two of them are affordable units.
One big issue from previous years was whether to allow apodments; what is the smallest size we should allow for new apartments? Many people who live alone would rather have a small unit in the city than a larger one that requires long commute times; other people who already live in these neighborhoods are concerned about increased density and parking. One issue that may be more pressing now is the "missing middle" for family sized housing. Now that we have a large number of people who are getting to the age where they want to settle down and raise families, is there going to be a place for them to do that in the city, or will they have to move further towards the outskirts where they can afford more space, but may need to live a more car-dependent lifestyle.
Like Seattle, King County is also updating its Comprehensive Plan, and trying to allocate growth among all of its cities and towns and unincorporated areas.
Seattle and King County should give climate a very high priority when updating their Comprehensive Plans. They need to come up with a plan that will make it easier for us to reduce emissions and housing costs and one that will factor in increased needs for resilience in the face of flooding, wildfires, and climate refugees.
Zoning Reforms Elsewhere in the Nation
Portland passed a zoning reform that makes 4 and 6-plexes legal in any residential lot in the city. The Urbanist has an article on it.
Tacoma is working on a zoning update, named Home In Tacoma. The Urbanist has an article on it: "Single-family areas would be redesignated and rezoned to Low-Scale Residential or Mid-Scale Residential zoning types, which would permit a mix of housing types like duplexes, rowhouses, and apartments."
Minneapolis passed a bill in 2019 allowing duplexes and triplexes on any residential lot. Here's a follow-up article on how it's going from Strong Towns: What if They Passed Zoning Reform and Nobody Came?
From Sightline, a round-up of zoning changes in the nation: Suddenly, Zoning Reforms are Popping Up Everywhere
This year, Washington and Oregon legalized people who aren't related to each other sharing housing in single family zones. See this article from Sightline: Oregon joins Washington to Allow Use of More Empty Bedrooms.