This article is the first part of a 4-part series examining the myriad benefits and feasibility of Colorado adopting the Advanced Clean Trucks and Heavy-Duty Omnibus rules in 2023.

Part 2: “Let’s ACT for Clean Trucks and Clean Air,” by Sarah Clark of Sierra Club

The rest of the series will be linked above as it becomes available – please check back!

It’s time for Colorado to step up and adopt the Advanced Clean Trucks and Heavy-Duty Omnibus rules to reduce greenhouse gas emissions and address climate change. Truck pollution threatens public health and our environment. These vehicles are responsible for an outsized share of climate pollution, and their harmful effects are shouldered disproportionately by low-income communities and communities of color. The reality on the ground in Colorado is alarming. We are not on track to meet our statutory climate goals, particularly in the transportation sector. If we continue down this path, we will not only miss our climate targets, but we will also harm the health and well-being of our communities. The time to act is now.


The proposed Advanced Clean Trucks and Heavy-Duty Omnibus rules are critical to reducing pollution from medium- and heavy-duty vehicles. By significantly reducing smog-forming pollution and establishing annual zero-emission vehicle sales requirements, we can produce billions of dollars in net economic benefits and slash greenhouse gas emissions. These rules are a win-win for our environment and our economy.

Climate Change Threatens All Coloradans

The impacts of climate change are already harming Colorado, and those impacts threaten to become worse. As Colorado’s Greenhouse Gas Pollution Reduction Roadmap summarizes, the climate change impacts Colorado faces now, and will face with increasing ferocity in the future, include decreased snowpack and earlier runoff; less water availability; lower water quality; risks of increased flooding; increased drought and drier soil; decreased crop yields; smaller herd size, increased impacts on trees and crops from insects, disease and drought; heat-related health risks; health impacts from ozone; increased risk of asthma and other respiratory diseases; increased risk of vector-borne diseases; wildlife population impacts; increases in invasive species; increased risk of wildfires; and increased area burned by wildfires. [1] These are impacts that affect our physical and mental health, ecosystems, agriculture, the recreation industry, and entire state economy.

Serious impacts of global heating have already reached Colorado. Western Colorado has warmed more than twice the national average, with 24 counties experiencing warming of 1.5-2.4 degrees Celsius. [2] The number of extreme heat days, the average state temperature, and the number and severity of heat waves have all increased. [3]

Higher temperatures associated with climate change have health implications for Coloradans. Extreme temperatures can cause heat stress/heat stroke and exacerbate asthma, kidney disease, cardiovascular disease, respiratory illness, and complications of diabetes. [4] As climate change continues and worsens, in a high-warming scenario the Southwest region of the US, including Colorado, is predicted to have the highest increase of risk of heat-associated premature deaths in the country. [5]

Rising temperatures increase the risk of drought: Colorado and the American West are experiencing the worst megadrought in 1200 years, [6] leading to impacts on agriculture, recreation, and health, and putting water sources at risk. The Colorado River Basin, which supplies 40 million people in seven states including Colorado, is in crisis, with water levels at historic lows, and a 30% risk of an unprecedented loss of hydropower generation from severely depleted Lake Powell and Lake Mead by late 2023. [7] Dust storms are made markedly worse by drought, impacting particularly the southeast, south-central and western slope regions of Colorado. [8] The increased particulate matter caused by blowing dust presents a health risk, and at high levels can be fatal. [9] [10]

In Colorado, the 20 largest fires in recorded history all occurred since 2000, with the three largest in 2020. [11] Colorado’s increasing wildfires are impacting health directly and indirectly. In addition to the obvious direct impacts of death and injury, they impact water quality, water supply, and increase deadly air pollution. [12] Wildfires cause heart and respiratory problems including lung cancer, chest pain, asthma and chronic obstructive pulmonary disease and also cause post-traumatic stress disorder, impacting mental health. [13] The number of Coloradans living in high risk, wild-land urban interface areas has more than doubled from 2000-2012 to over two million people. [14] Wildfires can also lead to polluted drinking water, as happened in Fort Collins in 2012 when fire-related debris, including cancer-causing trihalomethane, entered the water system. [15]

To avert more disastrous climate impacts on Colorado, every effort must be made to fulfill our statutory obligations to achieve emissions reductions consistent with Colorado’s greenhouse gas reduction goals.

Truck Emissions Contribute Significantly Climate-Altering Greenhouse Gases

Despite making up less than ten percent of the Colorado’s vehicles, medium- and heavy-duty vehicles are responsible for 22 percent of climate pollution from the transportation sector. [16] Like truck pollution, climate change impacts people of color and low-income communities disproportionately. The EPA found that low-income people and people of color are more likely to a) live in areas where they suffer health impacts from air quality associated with climate change (such as asthma onset for children and death from older adults), b) lose labor hours for extreme weather, and c) risk death from extreme temperatures. [17] A 2021 study shows that in U.S. cities, including in Denver and Colorado Springs, people of color are more likely to be exposed to heat intensity in urban “heat islands,” [18] and people with lower incomes and people of color are more likely to lack air conditioning. [19] In addition, vulnerable populations are more likely to be exposed to climate extremes at work, especially in outdoor jobs, and to lack adequate access to health care. [20] In these and other ways, climate change exacerbates existing health conditions for disproportionately impacted communities who have fewer resources to deal with them. Colorado law recognizes the disproportionate climate impacts that certain populations face, and directs the Commission to consider and prioritize rules and regulations which provide environmental and resiliency benefits to these communities. [21]

Colorado’s 2030 And 2050 Greenhouse Gas Reduction Goals are Moving Out of Reach

The passage of HB-1261 and SB-96 in 2019 put statutorily required GHG emission reduction goals in place for Colorado. Specifically, these bills required the state to propose and promulgate rules necessary to reduce GHGs 26% by 2025, 50% by 2030, and 90% by 2050 compared to 2005 levels. [22] The goals set in these landmark acts of the General Assembly should be the driving force in Colorado’s efforts to address climate change, and the AQCC has provided periodic updates on the progress of the state to reach these goals. The most recent August 2022 report demonstrated that the state is not on track to meet its interim and final GHG reduction goals—and transportation is the sector requiring the most attention. [23]

The table below, taken from the August 2022 report, [24] demonstrates the most updated GHG emissions by sectors, the anticipated reductions by 2025 from policies already implemented, and the 2025 target by sector to meet the statutorily required climate goals.

2025 GHG Reduction Estimates and Targets by Sector from GHG Regulations Adopted by December 2021
Sector Most Current Reported or Inventory GHG Emissions [25] (MMT CO2e) 2025 Reductions from AQCC Rulemakings (MMT CO2e) 2025 Target (MMt CO2e)
Electricity 31.4 9.1 21
Oil and Gas 20.26 4.9 + 2.4 13
Transportation 33.11 0.81 23
Residential, Commercial, Industrial Energy Use 27.81 0.12 26
Other 19.6 0.56 19.9


As the table shows, the transportation sector is in the most urgent need of emission reductions. To meet the interim climate goals, approximately 10 MMT of CO2e needs to be cut by 2025 to meet the sector targets outlined by the AQCC in December 2021. According to the report, AQCC actions will only account for 0.81 MMT of CO2e, or 8% of the needed reductions by 2025. The state is far enough off-track with transportation emission reductions that the 2025 GHG reduction goal in serious question, and the 2030 and 2050 goals will not currently be met. As the August 2022 AQCC report dryly put it, “for transportation, more work needs to be done.” [26]

Adopting and implementing the ACT Rule is work that must be done. M-HDVs are a significant contributor to Colorado’s GHG emissions and must be curtailed to meet the states’ climate goals.

Zero-Emission Trucks Can Help Slash Transportation’s GHG Emissions

The ACT Rule, once adopted, will contribute significantly to meeting Colorado’s GHG emission reduction goals. The benefits of this rule grow as the number of zero-emitting vehicles increases. The annual reductions are predicted to be 0.4 MMT of CO2e in 2030 and increase to 3.3 MMT of CO2e by 2050. In total, the rule is expected to lead to a cumulative reduction of 23.98 MMT of CO2e by 2050—an important element of the state’s GHG reduction strategy. While other complementary policies must also play a role in accelerating deployment of zero emission M-HD vehicles, the ACT Rule is a bedrock policy in this effort, which will ensure a reliable supply of vehicles and send a market signal to key stakeholders that the state is committed to its “larger goal of achieving a 100% [zero emission vehicle] transportation sector by 2050.” [27]

The benefits of transitioning to zero emission vehicles are amplified by deep emission cuts happening in Colorado’s electricity sector. As every unit of electricity becomes cleaner, so too does the fuel that is powering these vehicles, lowering the lifecycle emissions of these vehicles. All of Colorado’s major utilities are committed to reducing GHGs by at least 80% by 2030 compared to 2005 levels, [28] and some utilities are planning to go even further:  Tri-State Generation and Transmission and Platte River Power Authority have committed to 90% by 2030. [29] These deep cuts will greatly improve the lifecycle emissions profile of Colorado’s increasingly all-electric medium and heavy-duty fleets. Complementary emission reductions in the utility and transportation sectors will be critical to reaching the statutorily required GHG reduction targets and further the benefit of the ACT Rule.

We cannot afford to wait any longer. The climate crisis is here, and we must act now to protect our communities and our planet. Colorado’s Air Quality Control Commission must adopt the Advanced Clean Trucks and Heavy-Duty Omnibus rules and lead the way in building a cleaner, healthier, and more prosperous future for Colorado.

See references here