Colorado’s rule that promotes driving less and living more, explained

Why more states should follow Colorado’s example and adopt climate-friendly transportation policies

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Mackenzie Brown
Mackenzie Brown

Former Global Warming Solutions, Associate, Environment America

Matt Casale

Former Director, Environment Campaigns, PIRG

In the United States, transportation generates the largest share of greenhouse gas emissions- 27% of the total, more than electricity, industry, agriculture, or commercial and residential power usage. To reach our greenhouse gas emissions goals, we’re going to have to electrify our heavy, medium, and light duty vehicles. We’re also going to have to drive less. 

On July 15 of 2022, the Federal Highway Administration (FHWA) took a major step towards reducing the greenhouse gas emissions of our transportation system. The agency opened up a request for comments on a proposal similar to an Obama-era rule that had been repealed during the Trump administration, with a few significant changes. The rule requires state departments of transportation (DOTs) and metropolitan planning organizations (MPOs) to measure and report tailpipe emissions on the National Highway System, and to establish carbon dioxide targets for highway emissions that get stricter every year.

During the comment period, many individuals and organizations (including 18 states, 86 members of Congress, over 80 nonprofit organizations, 12 state attorney generals and tens of thousands of everyday citizens) commented in favor of the rule, agreeing that action is needed to decarbonize the transportation sector.

Environment America and U.S. PIRG were just a few of the many voices speaking out in support of the rule. We need to reduce our transportation emissions, and that’s much more difficult when we aren’t measuring them or making any sort of goals. Despite the fact that the proposed national rule lacks a binding enforcement mechanism, the requirement to measure emissions and set goals gives us higher quality information to use and puts climate on the transportation agenda. This is especially important in light of the billions of dollars of funding that the Infrastructure Investment and Jobs Act (IIJA) of 2021, is putting into the transportation system. This funding could improve our transportation system and make it more sustainable- or it could double down on our previous mistakes and increase emissions. This rule would help ensure that the funding is allocated to projects that use IIJA funding to make our infrastructure better and more climate-friendly- with an emphasis on making it easier to drive less, and drive electric.

While the comment period for this rule is now closed, the final rule has not yet been adopted. However, a number of states have already adopted similar rules that measure the greenhouse gas emissions of the transportation sector- 24 of them, plus the District of Columbia. One of the best, most comprehensive rules of this kind is the one Colorado implemented in December of 2021, as a requirement in its transportation funding bill (SB 260), the Colorado Greenhouse Gas Pollution Reduction Planning Rule. Here’s a breakdown of what it does.

The Colorado rule establishes greenhouse gas reduction goals for the Colorado DOT and Colorado’s metropolitan planning organizations (MPOs). It works by requiring these organizations to create plans that are projected to meet the greenhouse gas reduction targets. This can be done by limiting projects which will increase emissions via induced demand, such as new highways and road expansions, and by funding more projects which limit pollution and expand multimodal options- ways to get around without a car, such as walking, biking, and public transit.

The plans must demonstrate that emissions in the state and region stay within the established limits. If a plan fails to meet the target, the DOT and MPOs can implement measures like sidewalks, bike lanes, and improved public transit to mitigate the emissions. Individual projects that are placed in a transportation plan for approval are subject to these requirements- if a project that is expected to increase car travel is proposed, those submitting it for approval must show how they will mitigate that impact with these measures. If those submitting the proposal still can’t show that it will hit the emissions targets, even with mitigation measures, the Transportation Commission of Colorado can restrict the usage of certain funds. If CDOT can’t show that its plans hit the targets, it must use a larger percentage of its ten-year planning fund (a mix of federal and state dollars) on projects that reduce pollution, and if MPOs do the same, federal programs like the Surface Transportation Block Grant and Congestion Mitigation and Air Quality programs are put under similar restrictions.

In comparison to the national rule, the Colorado rule has some major advantages. One is that it is more enforceable. This is for two main reasons.

First, the Colorado rule goes beyond requiring organizations to set targets for their transportation emissions. Agencies must create plans that explicitly lay out how they will meet the targets. It goes even further by mandating that this be done on a project-by-project basis, stating that agencies must prove that a project will let them stay within the limits, and if it does not, they have to go back to the drawing board and add more mitigation measures.

Secondly, the Colorado rule states that if a proposed project doesn’t meet greenhouse gas targets even after more mitigation measures have been added, the Transportation Commission will restrict the submitter’s usage of certain funds and mandate that they only be used on mitigation measures.

Another aspect of the Colorado rule that is notable is that it aims to reduce the distance people drive. Even if we reach our vehicle electrification goals, to reach net zero transportation emissions, and to reduce the impact of mining for minerals for batteries, we will still need to drive less. Reducing vehicle miles traveled by making it easier for people to walk, bike, and take public transit for more trips has other benefits as well. Benefits like more physical activity, less pollution from tires, and less natural space taken up by roads and parking lots are just a few of the ways that driving less can make our lives better.

The Colorado rule also applies to a much broader set of roads than the proposed national rule. The national rule would apply to highways within the National Highway System- which ultimately represent only 4% of all roads. The Colorado rule applies to all the roads managed by the Department of Transportation in the state, as well as roads managed by MPOs.

Historically, the transportation planning system in the United States has focused on the goal of moving cars from location to location as quickly as possible, with as little congestion as possible, with the safety of those in cars as the primary priority. This has led to infrastructure supporting transit, walking and biking receiving fewer resources in comparison to costly and unnecessary highways and road expansions which often don’t solve congestion, but do cause people to drive more. Despite pressure from transportation advocates, this philosophy has remained largely unchanged for decades. This rule acts as a much-needed corrective to this type of thinking. It’s estimated that this rule will reduce VMT by 6-9%.

When it comes to infrastructure, even transformational changes tend to happen slowly, in years rather than months. But we’re already seeing positive impacts from Colorado’s rule.

It’s behind the cancellation of a potentially disastrous expansion of highway I-25, and the shifting of those funds towards five bus rapid transit projects. And it’s led to billions of dollars in future funding being transferred from highway expansions and towards infrastructure to support walking, biking, and transit.

The national greenhouse gas rule is yet to be implemented. But there’s a lot states can do to improve their transportation system, with or without it. 

A number of states have existing laws on the books seeking to address the climate impact of our transportation system, but all of them could be stronger. We urge every state, whether or not they have an existing rule on the books, to adopt strong greenhouse gas rules with measures based around some of the things that make the Colorado rule effective.

States should go beyond requiring DOTs and MPOs to set targets for transportation emissions, and actually mandate plans that demonstrate how they will hit these targets. Even better when the plans are on a project-by-project basis.

In addition, the fact that the Colorado rule has enforcement for the targets, in the form of potential funding restrictions if CDOT or MPOs are not on track, bolsters its effectiveness even more.

There’s other provisions that could make Colorado’s rule- and those of other states- more effective as well.

Setting a goal of actually reducing VMT, not just reducing its rate of growth, is a provision in line with the kind of changes we need to make in our transportation system.

Urban infill development is one of the most effective strategies governments can use to reduce carbon emissions, and plans that incorporate this strategy are likely to see sharper reductions in emissions by not only making walking, biking, and transit more feasible, but also reducing the distance people have to drive to access basic goods and services. State and local transportation agencies should work with local governments to encourage improvements that will help meet GHG and VMT reduction goals.

Privatized highways- like toll roads- should be included in calculations. 

Introduce policies that end urban highway expansions. The cancellation of the I-25 expansion was a positive outcome. If we want to reduce VMT and the climate impact of our transportation system, we need to “do no harm” and stop inducing demand and destroying communities with these kinds of projects.

We need to radically change our transportation system, for the sake of our climate and for those who aren’t able to reach critical services in our current system. Colorado’s rule and the potential national rule are both exciting developments, and big steps forward. But we can go even further- in all 50 states- in legislating a transportation system that works for everyone, with or without the national rule.


Mackenzie Brown

Former Global Warming Solutions, Associate, Environment America

Matt Casale

Former Director, Environment Campaigns, PIRG

staff | TPIN

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