Fly into Denver International Airport (DIA) in the daylight and you can look down on acres of open land being groomed for sprawling single-family development. In 2021, over ¾ of lots under development in the Denver region were in Adams, Arapahoe, and Douglas Counties, mostly single-detached homes built on undeveloped land far from jobs, shopping, and other destinations. This type of low-density, auto-centric growth is incompatible with Colorado’s air quality and climate goals, and will only increase congestion, pollution, land and water consumption, and household transportation costs. In fact, greenhouse gas (GHG) modeling from the Denver Regional Council of Governments (DRCOG) and Colorado Department of Transportation (CDOT) shows that we need to flip the script and locate 75% of new housing and jobs in mixed-use, transportation-efficient neighborhoods to reduce vehicle travel and meet our 2030 climate targets.
Colorado is dealing with multiple intersecting crises on air quality, climate, and housing affordability. On the environmental side, the two-headed monster of highway expansion and suburban sprawl has helped make transportation the “king of pollution” for both GHG emissions and ozone. As we’re learning the hard way in Colorado, it’s very difficult to reduce vehicle pollution and congestion in a world built for cars, entrenched by decades of auto-centric land use decisions. To quote one of my favorite transit planners, Jarrett Walker, “if you’re just focusing on transportation and not land use, you’re looking at the tail, not the dog.”
Local zoning and housing policies shape our communities and determine where we travel, how we travel, and how much it costs to get around. When these regulations prevent infill development, they push growth into car-dependent suburbs, which leads to more traffic and forces agencies like CDOT, DRCOG, and local governments (and taxpayers) to pick up the tab, spending precious transportation dollars on expensive highways and giant parking lots. In contrast, when communities embrace mixed-use, compact development and pair it with investment in multimodal transportation options, they reduce vehicle trips and pollution.
Inefficient land use and local growth limits have also restricted housing supply, leading to historic increases in housing costs, including a 24% increase in Colorado home values in just the last year. Colorado is now 325,000 housing units short of a stable market and needs to double the rate of annual production from 26,500 to 54,000 new units per year to meet demand and reduce housing costs.
Surveys show that people want a greater diversity of housing options like duplexes, triplexes, townhomes, apartments, and Accessory Dwelling Units (ADUs). Yet, nearly 80% of land in the City of Denver is restricted to one dwelling unit per parcel, a policy that constrains housing supply and promotes sprawl.
To clean our air, lower housing costs, and improve access to opportunity, communities in Colorado must adopt land use policies that promote infill development and support more walkable and transit-friendly communities. Land use policies take time to mature, so now is the time to update our zoning and housing policies — before we add another three million people to our state by 2050 and further lock ourselves into more expensive and high-polluting development patterns.
Colorado’s plan to tackle GHG pollution from transportation
According to the state’s GHG Pollution Reduction Roadmap, Colorado needs to reduce GHG emissions from transportation by 40% by 2030. A highly-optimistic electric vehicle (EV) scenario, where we increase the number of EVs on our roads from 55,000 today to nearly one million by 2030, will get us ⅔ of the way to our 2030 target. The remaining third must come from fewer and shorter vehicle trips resulting in a 10% reduction in Vehicle-Miles Traveled (VMT) per capita or about 20 fewer miles per week. Many of us would like the freedom to choose between multiple safe, convenient, and affordable travel options. For others, it’s a necessity and in a typical community, 20-40% of travelers do not or should not drive either because they’re adolescents, seniors, people with disabilities, or low-income households that can’t afford a vehicle.
Expanding travel options and reducing VMT requires two things: 1) Significant investment in transit, bicycle, and pedestrian infrastructure, and 2) Building housing, jobs, schools, and other activities close together to shorten trips lengths and enable transit, biking, and walking (the average walking trip is 0.7 miles and bicycling trip is 2.3 miles). We should recognize these are two sides of the same coin.
When housing densities reach 10-12 dwelling units per acre (compact single-family homes, duplexes, and townhomes) near an activity center with jobs, schools, parks, and retail, dependence on cars begins to decline and people begin to walk, cycle, or take transit. Higher levels of mode shift occur when housing density exceeds 20 dwelling units per acre (multiplexes and low-rise apartment buildings), and employment density reaches 25-50 jobs per acre.
Figure 2: Transportation for America’s Driving Down Emissions report illustrates how people can access the same number of activities with a fraction of the VMT in a clustered development pattern compared to sprawl.
To identify potential pathways to meet our climate and VMT reduction targets, DRCOG modeled a series of transportation and land use scenarios in their 2050 Metrovision. Their “Transit” scenario assumes we invest an additional $36 billion in transit by 2050, resulting in a 2% decrease in VMT per capita against the baseline forecast — not nearly enough to meet our targets. However, when the Transit scenario is combined with a “Centers” land use scenario, which focuses 75% of new housing and job growth in urban centers and transit corridors, the result is a 24% VMT reduction, three times as many walk and bicycle trips, and six times as many transit trips. The upshot is that the expansion of public transit is almost 10 times more effective in reducing GHG pollution when coupled with transportation-efficient land use.
The potential for VMT reduction is even more dramatic when we couple affordable housing with transit, also known as Equitable Transit-Oriented Development (eTOD). A 2020 study from the Regional Transportation District (RTD) found that only 39% of residents living in affordable housing near RTD transit stations own a car and 63% ride transit at least once per week. In contrast, 93% of residents of market rate housing near transit own cars and 18% take the bus at least once per week. RTD used this study to inform their new Equitable TOD Policy, which sets a 35% affordable housing goal for RTD-owned TOD and allows developers to lower the number of parking spaces depending on projected utilization.
eTOD not only provides affordable housing for those who need it, but also improves access to jobs and helps low-income households to save money on transportation, the second highest monthly expense. Any climate-friendly land use policy must be designed in a way that advances equity by preserving affordable housing opportunities in disproportionately-impacted communities.
Land use is one of the most impactful tools local governments have to tackle climate change
Communities across Colorado are taking action on climate by developing Climate Action Plans, launching clean energy initiatives, and advocating for stronger federal and state policies. However, very few have acknowledged the potential for land use reforms to reduce GHG pollution, despite the fact that infill development is one of the most impactful things that local governments can control to combat climate change.
There are a number of ways that local governments can support urban infill:
- Update zoning to enable more compact, mixed-use development;
- Establish density minimums, particularly along transit corridors and near commercial centers;
- Allow 2-4 dwellings units on single-family lots with a density bonus for affordable housing;
- Allow ADUs by-right on all single-family lots;
- Increase or eliminate occupancy limits;
- Lower or eliminate parking requirements or institute parking maximums instead of parking minimums;
- Upzone all property within 1⁄4-mile of high-frequency transit stations to allow mixed-use development with requirements for eTOD;
- Streamline the permitting and approval process for affordable housing and compact development;
- Institute Transportation Demand Management Ordinances for new development to include EcoPasses, unbundled parking, bikeshare subscriptions, and other vehicle trip reduction strategies; and/or
- Reduce maximum single-family home sizes.
Allowing multiple modest homes on a lot that was previously zoned for a large single-family home would not only reduce GHG emissions, but would also promote affordability. For example, imagine replacing an $800,000 single-family home with a duplex with each home selling for $450,000.
It’s important for local governments to understand the relationship between growth and climate change. In many cases, encouraging infill development in a community may have the effect of increasing citywide emissions, which may run counter to local GHG reduction goals. However, when it comes to global pollutants like GHGs, the carbon intensity in a particular city doesn’t matter and the goal must be to minimize total GHG emissions period, regardless of where they come from. This means encouraging growth patterns that enable below-average household carbon footprints and lower total emissions, even if it means higher emissions within a narrow geographic boundary.
To give some regional examples, Denver, Englewood, Boulder, and Wheat Ridge have relatively high transportation GHG footprints of roughly 30-40 tons per acre, but GHGs per household are relatively low at 6-7 tons per year because they have higher population densities and better job access. In contrast, lower-density communities like Parker, Brighton, Castle Rock, and Highlands Ranch produce 15-20 GHGs per acre, but transportation GHGs per household are well over 10 tons per year. Directing growth to areas with fundamentally lower per-capita emissions, as opposed to areas with high emissions, can lower overall pollution. Accordingly, local governments should set climate, VMT, and land use goals to incentivize climate-friendly housing and zoning policies.
The DRCOG region expects to add 225,000 new homes by 2030 and where we locate those homes will largely determine whether we meet our climate and air quality goals. For example, building all 225,000 homes in transportation-efficient areas with lower transportation GHGs per household would save nearly 406,000 metric tons of GHG pollution per year, the equivalent to taking 88,000 gas-powered cars off the road in 2030 compared to a business-as-usual scenario. This alone would get DRCOG about halfway to their GHG reduction target of 820,000 metric tons by 2030.*
However, many local governments are not making the decisions necessary to maximize transportation efficiency and minimize pollution. For example, consider current plans to expand development onto the eastern plains, south of DIA. As part of future development plans in northeast Aurora, planners envision a brand new sprawling community of 50,000 new homes and 82,000 jobs on 123 square miles of farmland, far from any existing destination centers or transit routes (see Google Maps image below).
While planners have taken steps to co-locate housing and jobs in some areas, the majority of land is zoned for single-detached homes where the density will not be high enough to justify frequent transit service or support walkability, meaning residents will likely have to drive everywhere. Residents who have jobs in downtown Denver or the Denver Tech Center will likely drive 50-60 miles round trip for work, over twice the daily average for the Denver region, bringing more traffic and pollution into urban communities that are already struggling with the health impacts of poor air quality.
In addition to more vehicle pollution and land consumption, these greenfield developments exacerbate Colorado’s water challenges. Residents of large single-unit homes use about twice as much water as those living in multi-family homes.
The northeast Aurora development plan would come at a massive cost to Colorado, including a $2.2 billion price tag for 168 new miles of road to serve these new suburban communities. (For reference, Colorado’s annual transportation budget is about $1.5 billion for the whole state.) These land use decisions are neither financially nor environmentally sustainable for our region.
Figure 6: The Northeast Area Transportation Study (NEATS) from 2018.
It’s clear that people want to live in compact, walkable neighborhoods where they can step out their front door and safely walk to a park, grocery store, restaurant, or weekend farmers’ market. Surveys show about half of US residents would prefer to live in walkable neighborhoods even if it meant living in a smaller home. Real estate companies have even developed a Walk Score metric to quantify the economic value of walkability. On average, a 1 point Walk Score boost, indicating a higher level of pedestrian friendliness and proximity to amenities, is worth up to $3,000 in home value. These are highly desirable places to live, yet we restrict their development.
Examples of walkable and transit-oriented communities in Denver and Boulder.
Rethinking how we govern land use in Colorado
Every community in Colorado has an interest in providing a stable climate and affordable housing for its residents. However, not every community decision aligns with those interests. For example, communities like Boulder, Lakewood, and Golden have adopted citywide residential growth caps and other restrictive housing policies that effectively make homes less affordable, promote sprawl, increase car dependence, drive up pollution, and increase our cost of living.
In just the last month, new housing proposals in Vail, Glenwood Springs, and Littleton have been denied because of pushback from anti-growth community members. In most cases, local governments are only hearing from residents who already enjoy the benefits of living in their communities and not the unrepresented who are forced to drive long distances to work in towns that don’t have adequate or affordable housing. (A recent study from Massachusetts found that only 14.6% of people who attended local community meetings were in favor of the relevant projects.)
These local decisions have impacts beyond their own borders because we live in an interconnected society of residential communities, job centers, universities, downtowns, parks, and other destinations. One community's failure to address their own housing needs makes it more difficult for neighboring communities to provide affordable housing for their own residents.
Colorado needs to rethink how it governs land use to better balance local concerns about growth against the overall statewide interest in preserving a stable climate, providing affordable housing, and equitably improving quality of life.
Other states have been active on land use and housing reform over the last several years. In 2019, Oregon legalized duplexes, triplexes, and fourplexes by-right in residential areas in larger cities. (A study from Sightline Institute found that allowing multiplexes on a city block can cut carbon emission per household by 20%.) Massachusetts passed a bill requiring local governments to provide multi-family housing around high-frequency transit stations. Utah passed a pair of bills tying transportation funding to efficient land use policy to increase the supply of housing. The main argument from Republican bill sponsors in Utah: Do you want your children and grandchildren to be able to live here in the future?
CDOT and Metropolitan Planning Organizations might also take a page from the Biden Administration’s updated housing and transportation grant programs, which now include criteria for smart land use and location-efficient affordable housing. The U.S. Department of Transportation recently updated the Rebuilding American Infrastructure with Sustainability and Equity and Safe Streets for All programs to reward projects that “support fiscally responsible land use and transportation efficient design” and “reduce transportation and housing cost burdens, including through commercial and mixed-income residential development near public transportation, along rural main streets, or other walkable neighborhoods.”
Colorado is making some progress on land use and housing. In 2021, the Colorado legislature passed House Bill (HB) 1271 with incentives for local governments that adopt sustainable land use and zoning policies. Earlier this month, the legislature passed HB22-1304, creating the “Strong Communities Grant Program” with a competitive “race to the top '' award structure, where local governments that do the most to increase the supply of affordable housing in downtown areas and near transit are prioritized for local infrastructure grants. The bill promotes strategies such as allowing ADUs and multiplexes in residential neighborhoods, zoning for mixed-use higher density development in downtown areas and near transit, and reducing parking requirements to allocate more space for housing instead of parked cars.
The Colorado legislature also passed a series of affordable housing bills this year to subsidize and finance the construction of about 2,000 income-restricted units per year. These investments will be critical to support low-income housing, but they won’t do enough on their own to address the statewide housing shortage, improve the overall affordability of the housing market for all income-levels, or promote transportation-efficient land use patterns.
While these new policies will help, creating abundant and affordable housing opportunities for all Coloradans will require more transformative land use and zoning policies. In addition to incentives for local governments to adopt sustainable land use practices, Colorado should be looking at policies that require local communities to provide affordable housing and improve community design to make our cities more efficient, more equitable, and better places to live.
The climate crisis and our housing crisis are urgent and intersecting priorities. Solving these challenges will require productive engagement from every group, every community, and every resident in Colorado. The time to act is now.
*The Center for Neighborhood Technology’s Household and Transportation Affordability Index estimates average annual transportation-related GHG emission per household for each municipality in the U.S. To estimate the GHG reduction potential for smart land use strategies in the DRCOG region, we subtracted the below-average emissions profile (6.5 tCO2/year) from the regional average (8.5 tCO2/year) and multiplied by the projected number of new housing units by 2030 (224,300 homes), then converted from tonnes to metric tons and compared to the GHG reduction targets established by CDOT’s GHG Planning Rule.
Matt Frommer is Senior Transportation Associate at SWEEP. You can follow him on Twitter.