Transportation GHG Emissions: What Denver Can Learn from Other Cities

Fare-free transit in Kansas City (Martin Cizmar, Kansas City Magazine)

Erin Nobler is a PhD student in the College of Architecture and Planning at CU Denver studying transportation planning, equity, and energy. 


High single-occupancy vehicle use and a rapidly increasing population in Denver means that our city creates on the order of 2.5 million metric tons (or approximately 5.5 billion pounds) of private transportation-related greenhouse gas (GHG) emissions each year. How can we possibly mitigate emissions while also ensuring transportation mobility within the city?

The typical response usually starts with a long, drawn-out planning phase. However, as we’ve seen in recent weeks, many positive actions can be accomplished quickly and inexpensively (Seattle Times). So rather than embark in a lengthy and expensive study that may only collect dust on a shelf, Denver can act now, informed by what cities around the world have already learned.

To help with these efforts, I estimated the potential effectiveness of various policies – such as congestion pricing, increased parking fees, transit priority, fare-free transit, and increased transit service – based upon a combination of the best existing literature and empirical evidence[1]. I then applied these estimates to a Denver-specific baseline (created using a combination of data from the U.S. Department of Energy, and Oak Ridge National Laboratory) to determine the possible impacts shown in the table below. What I found is that these strategies could reduce Denver’s emissions anywhere from about 100,000 to 850,000 tons of Carbon Dioxide (CO2) annually. This could account for a reduction of anywhere from 4-34% of GHG emissions from light duty vehicles every year.

Screen Shot 2020-05-26 at 3.11.27 PMThere is no silver bullet. Rather than considering any of these policies individually, we need to be thinking about a suite of changes. For instance, Denver could consider congestion or parking pricing in combination with expanded bus service, enhanced bike and pedestrian infrastructure, increased parking fees within the cordon zone, and expanded park-and-ride facilities outside of zones. As with any policy change, there are often unintended consequences to consider. Revenue from congestion or parking pricing could support multimodal infrastructure investments. Discounted transit fares or fare-free transit could help limit any real or perceived financial burden on low income or transit-bound residents. Elimination of fee collection on transit has the added bonus of speeding up service while limiting interactions with drivers, a step that has already been temporarily implemented by RTD during the COVID-19 pandemic.

Looking beyond explicit transportation policy, consideration should also be given to the impact on increased housing prices for Denver’s already limited inner-city affordable housing stock. Coordinated housing policy could help limit the displacement of current residents, which would result not only in gentrification, but subsequent increases in single occupancy vehicle emissions from longer commutes from the suburbs into the inner-city.

Big picture: discussion and action on these policies can occur now. We have enough information to start conversations on which policies make the most sense for Denver and its residents. Using existing information from current programs can fast track these discussions and move us towards real and lasting impacts on the city.


[1] Albert and Mahalel, 2006. Link

Transport for London, 2004: Link

Eliasson et al., 2006: Link.

Federal Highway Administration, 2008: Link

Tri-State Transportation Campaign, 2018: Link

Peng et. al., 1996. Link

Ben-Dor et. al., 2017: Link

Litman, 2017. Link

Litman, 2008: Link

Volinski, 2012: Link

Transport for London, 2004: Link

Peng et. al., 1996. Link


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