Environment
One of the largest contributors of greenhouse gas emissions in the US is the transportation sector, especially light-duty passenger vehicles and trucks. Providing active transportation options such as walking, bicycling, and transit can decrease motor vehicle usage and dependency on nonrenewable resources, reducing greenhouse gas emissions and air pollution. Integrating considerations for environmental impacts when planning for pedestrian and bicycle infrastructure can also help reduce stormwater and mitigate flooding.
Climate change and environmental impacts are intrinsically linked to broader concerns related to health and equity. The people who suffer the most burden of climate change or environmental impacts usually contribute the least greenhouse gas emissions, and current mitigation strategies in transportation, such as access to goods and services via low-carbon transportation, walking, or biking tend to be more readily available in higher-income areas.
Greenhouse Gas Emissions and Climate Change
- According to the United States Environmental Protection Agency, the transportation sector accounted for the largest share of greenhouse gas emissions (28%) in the United States in 2018. Light-duty vehicles, which includes passenger vehicles and light-duty trucks, account for the majority of transportation sector emissions at 59%. Vehicle emissions are determined by fuel efficiency, carbon content of fuel, and vehicle miles traveled.
- Journal article The Climate Change Mitigation Effects of Daily Active Travel in Cities in Transportation Research Part D: Transport and Environment explores how much carbon dioxide can be saved by walking, and bicycling, including e-bikes. Researchers collected travel activity data in seven European cities and derived life cycle carbon dioxide emissions across modes and purposes. Among other findings, researchers found that people who bicycled every day had 84% lower carbon dioxide emissions from all daily travel than non-cyclists.
- A New York Times article in 2020 reports that transportation sector greenhouse gas emissions declined by 14.7% in 2020 as millions of people decreased driving and cancelled airline flights. In the US, people drove 15% fewer miles over 2020 than they did in 2019, and jet fuel use decreased by one-third during the same time period.
- Journal article Improving the Representation of Modal Choice into Bottom-Up Optimization Energy System Models: The MoCho-TIMES Model in Applied Energy concludes that providing alternatives to car for traveling (like biking and walking), building new infrastructure, improving the quality and accessibility to public transport, especially in rural areas, and establishing effective taxation and incentive schemes could cut transportation-related carbon emissions in half by 2050.
- A 2015 report from the Institute for Transportation and Development Policy describes how a High Shift Cycling scenario with a strong cycling emphasis can reduce urban transport emissions by 11% by 2050.
- An article from Inside Climate News describes car culture in Germany and how the transportation sector can help the country meet ambitious targets for reducing greenhouse gas emissions via mobility shifts to public transportation, walking, and biking. The article shares comparisons between modes of transportation in Germany and in the US, using data from the USDOT National Household Travel Survey and the Germany Federal Ministry Transport's Mobility in Germany report.
City and Town Climate Action Plans with Active Travel Initiatives
Communities across the US have recognized the connections between transportation, climate and the natural environment, and created plans to address these challenges head-on. Some examples include:
- Cambridge, Massachusetts Climate Action Plan acknowledges that the city already contains high levels of public transit and active transportation use yet continues to promote infrastructure, road design, facilities, and policies which encourage active or shared/public transportation.
- Carson, California Climate Action Plan plans to add solar-powered lighting and vehicle speed feedback signs near crosswalks to promote traffic calming and encourage active transportation.
- Hartford, Connecticut Climate Action Plan aims to increase walking and biking through improving and testing Tactical Urbanism infrastructure changes (parklets, lane striping, buffers), establishing an affordable bikeshare program, and improving safety and bike repair education.
- Minneapolis, Minnesota Transportation Action Plan intends to increase pedestrian trips from 16% to 25% by 2030 through nine strategies that promote a safe and inviting walking and rolling environment. Strategies also focus on enhancing visibility at pedestrian crossings, increasing street lighting, and making other improvements along a designated Pedestrian Priority Network. The plan also includes a goal to increase bike trips from 3% to 10% by 2030. The city will do this by establishing an All Ages and Abilities Network which includes protected lanes and physically separated trails from motorized vehicles and improved intersection crossings and year-round accessibility.
- San Diego County, California Climate Action Plan includes a goal to improve multi-modal use of roadways by improving 700 centerline miles of roadway segments, including 250 intersections and 210 lane miles of bikeway improvements by 2030, and an additional 500 centerline miles of roadway segments, including 250 intersections and 210 lane miles of bikeway improvements by 2050.
- San Francisco, California Transportation Sector Climate Action Strategy includes a goal of shifting 80% of all trips to bicycling, walking or transit by 2080 by continuing to implement its Transit-First Policy and engaging with businesses, employers and residents to encourage active transportation.
- Seattle, Washington Climate Action Strategy sees the potential for an 8-12% reduction in transportation emissions (5.5-8% overall) by implementing congestion pricing coupled with investing in expanded transit and electrification in underserved communities.
Local and regional investments in transit and bike and pedestrian infrastructure have led to significant reductions in single occupant vehicle (SOV) use in Seattle. The period when Seattle has experienced some of its most rapid growth, 2010-2017, has also seen significant progress in commuter mode shift toward more sustainable modes of transportation. During this seven-year period, downtown Seattle has added 45,000 jobs and become more residential, but only 2,255 new drive-alone trips have been added to downtown streets. The overall SOV mode share of commuter trips declined by 10 points to 25% and the share of transit trips has steadily increased from 42% to 48%. Meanwhile, walking to work increased 1.8 basis points to 7.7% and the bike share grew to over 3%.
Environmental Impacts Relating to Air and Water
- Building infrastructure for vehicles, such as streets and parking lots, increases the impervious surface of an area which can exacerbate stormwater runoff, urban flooding, and the urban heat island effect. Promoting pedestrian and bike infrastructure provides an opportunity to integrate green infrastructure into street design and produce co-benefits for urban heat island, stormwater, and flood mitigation as well as pedestrian health and safety.
- Journal article Cyclists' Personal Exposure to Traffic-Related Air Pollution and its Influence on Bikeability in Transportation Research Part D: Transport and Environment considers cyclists' exposure to traffic-related air pollution via a comprehensive bikeability index that comprises four subindices: accessibility, suitability, perceptibility, and prevailing air quality in the vicinity of cycling routes. Including air quality makes a significant difference when calculating a bikeability index.
- Journal article Estimates of Pedestrian Exposure to Atmospheric Pollution using High-Resolution Modelling in a Real Traffic Hot-Spot in Science of The Total Environment estimates the exposure of pedestrians to ambient nitrogen oxides (NOx) concentrations with high spatial resolution in a real urban traffic hot-spot under different methodologies.
- Journal article Disparities in PM2.5 air pollution in the United States in Science finds that the spatial distribution of fine particulate matter concentrations has remained largely unchanged over 36 years. Although fine particulate pollution levels have dropped overall, those areas that were most and least polluted in 1981 remain so today.
- Journal article Association of the Combined Effects of Air Pollution and Changes in Physical Activity with Cardiovascular Disease in Young Adults in European Heart Journal suggests that exercising outdoors beyond recommended amount when air pollution levels are high may offset potential health benefits among adults 20 to 39 years old. Shows that air pollution is associated with increased cardiovascular risk.
Co-Benefits of Investing in Walking and Cycling
- Journal article Climate Policy Co-Benefits: A Review in Climate Policy describes the co-benefits that can accrue from replacing car trips by biking and walking, including enhanced public health, improved air quality, reduced traffic injury, and lower greenhouse gas emissions.
Additional Resources
- A 2020 report from Smart Growth America and Transportation for America Driving Down Emissions: Transportation, land use, and climate change explores how land-use and transportation decisions are connected and introduces five strategies that can impact greenhouse gas emissions and help build a more equitable society. The report includes hidden environmental impacts of driving and other environmental concerns, and references specific concerns about older adults, people of color, and people walking in low-income communities who are disproportionately represented in fatal crashes.
- A Green New Deal for City and Suburban Transportation from Transit Center, Transportation for America, and the McHarg Center discusses Federal transportation policy and cites statistics and facts for background. The report also provides recommendations to reduce greenhouses, including building Complete Streets and prioritizing roadway maintenance to ensure road projects meet environmental goals.
- USDOT hosts a website of case studies of MPO activities that include sustainability and greenhouse gas mitigation plans.
- FHWA's Handbook for Estimated Transportation Greenhouse Gases for Integration into the Planning Process provides information on how to analyze on-road greenhouse gas emissions at the state and regional level and incorporate those analyses into the planning efforts. This analyses and project planning may be helpful in thinking about potential offsets in introducing active transportation projects.
- StreetSmart maintains a list of strategies and resources related to greenhouse gas emissions in the context of transportation.
- Good to Go? Assessing the Environmental Performance of New Mobility from International Transport Forum examines the climate impact of personal and shared electric kick-scooters, bicycles, e-bikes, electric mopeds, as well as car-based ride-sharing services. Analyzes the life-cycle performance of a range of new vehicles and services based on their technical characteristics, operation and maintenance, and compares it with that of privately owned cars and public transport. Identifies solutions to make new mobility a useful part of the urban transport mix while helping to reduce energy use and limit climate change.
- Journal article The E-Bike Potential: Estimating Regional E-Bike Impacts on Greenhouse Gas Emissions in Transportation Research Part D: Transport and Environment uses data from a survey of e-bike owners to adapt and augment a mode replacement model to consider the case of Portland, Oregon for various levels of e-bike person miles traveled (PMT) mode share penetration.
- San Diego, California Prioritizes Community-Based Partnerships to Develop Environmental Justice Mobility Toolkit article in FHWA's Fostering Multimodal Connections describes a community-based partnership driven project to develop mobility solutions for an environmental justice neighborhood that lacked adequate bicycle or pedestrian infrastructure. It also includes an existing conditions assessment, and development of a comprehensive Mobility Solutions Toolkit, and a shorter Mobility Solutions Playbook (in both English and Spanish).
- Advancing Climate, Safety, and Equity Goals by Putting Pedestrians First in ITE Journal Active Transportation Issue covers the city of Minneapolis, Minnesota Transportation Action Plan which guides planning, design, and implementation of transportation projects via a framework that emphasizes equity and commitment to addressing climate change by focusing on low or no-carbon transportation options.
Tools
- C40 Cities offers an Excel-based Adaptation and Mitigation Interaction Assessment (AMIA) tool to help city practitioners plan for climate action by mapping synergies between projects such as electric buses or building greenways for active travel. It also includes case studies and examples that include greenway developments in coordination with other projects.
- The Energy Policy Simulator from Energy Innovation LLC estimates environmental, economic, and health impacts of dozens of climate and energy policies. It produces clear cost and emissions figures via an interactive tool. Within the tool, there is an option for mode shifting which represents measures aimed at reducing demand for passenger vehicles by shifting to transit, walking, biking, or eliminating trips completely.
- Air Quality Aware, an app from Esri that uses data from the federal government to provide information on current air quality, how it might change in the future, and its impacts on local communities and vulnerable populations.
- A Traffic-Related Air Pollution: Emissions, Human Exposures and Health Course from Center for Advancing Research in Transportation Emissions, Energy and Health, shares a six module, cross-disciplinary graduate-level course for students and practitioners in the fields of transportation, environmental health, and planning and policy-making. Participants will learn about road traffic, vehicle emissions, traffic-relater air pollution, human exposure, biological mechanism, associated health effects, and population-based impacts.
