Most Recent Clean Air Case Studies

Proffers for New Development in Fairfax County, Virginia  

Fairfax County established Transportation Demand Management (TDM) requirements (“proffers”) for new development that would have significant traffic impacts. For buildings within the urban centre of Tysons, trips had to be reduced between 25% and 65% during peak hours, depending on the size of the building and its proximity to the Metrorail stations. The county proffers required large new properties to annually monitor trips, conduct tenant commuting surveys, and show that they were meeting their trip reduction goals. They also had to conduct surveys every three years. Over seven years, 13 such developments generated 63% fewer trips, which was 34% beyond their goals. For the office buildings, this was likely at least partly a result of more people working from home during the COVID pandemic.

Carpooling Promotion in Paris  

France provides financial incentives to local travel authorities (LTAs), employers and employees to promote carpooling. It also funds the development of carpooling infrastructure, ridesharing platforms that make it much easier to carpool, and fraud prevention mechanisms. This case study covers the formative research and early implementation in Paris of France’s National Daily Carpooling Plan.

Smart Trips Austin  

Smart Trips Austin encourages residents of Austin Texas, USA to take multi-modal transportation options (walk, bike, ride transit, and share rides) more often, rather than drive alone. The program focuses on personal interactions — educating individuals on their options and overcoming barriers to multi-modal travel. Smart Trips reinforces this new information using community-based programs such as learn-to-ride classes, transit instruction, and group walking activities. Initially, the program targeted residential neighbourhoods of Austin Texas; each year a different area was targeted. In 2020 the program expanded to city-wide and began to segment using a Stages of Change approach. In 2021, it started targeting residents who had recently moved to or around Austin. Smart Trips Austin averaged a participation rate of 5-10% of households contacted, a 5-10% reduction in drive-alone trips among participants (about 41,000 vehicle trips per year), and a corresponding 5-10% increase in active and shared trips. This account of the program was designated a Landmark case study in 2023, making the City of Austin one of the few governments with more than one program designation. 

Co-Ownership of Wind Farms  

What if you want to move away from gas and oil, but rent, are about to move, or can’t afford solar panels? If your energy supplier has not already pledged to go green, you have few options. The co-ownership of wind farms engages and makes it practical for more homeowners and renters to buy wind-generated power.

Liftshare and Mobilityways, U.K.  

Liftshare is a social enterprise that has worked with over 700 of the UK’s largest employers to reduce the number of single occupancy vehicle trips using carsharing, active transportation and public transit when commuting for work. With an online community of over 1 million members, it is estimated that Liftshare members have avoided the release of 300 million kg / 300,000 tonnes of commuter carbon emissions (averaging 50 million kg / 50,000 tonnes per year). In 2020, Liftshare launched Mobilityways, a sister platform that enables employers to evidence, track, plan and change their commuter emissions via a set of tools / modules that work seamlessly together.

How Copenhagen Became a Cycling City  

What makes a great cycling city? How did the medium-sized City of Copenhagen get its citizens to cycle to work / school 49% of the time? While topography and climate are significant influencers, safety, supportive infrastructure, and promotion also played key roles. Copenhagen increased cycling by making it safer, easier, and more convenient. This case illustrates the power of piloting alternative enhancements on an ongoing basis to further reduce barriers and increase benefits, based on regular surveys, traffic data and safety data. It also features a transparent planning process - the Bicycle Account – a research, evaluation, promotion, and citizen engagement tool used every two years since 1996. Designated a Landmark case study by our Transportation peer selection panel in 2022.

Paris Reduces Car Use, Boosts Walking and Cycling  

Paris is an inspiration for large cities around the world, having reduced car traffic in its core (Ile de France) from a mode share of 12.8% in 2010 to 6% in 2020. How did Paris get to be one of the cities in the world with the lowest mode share for single occupant vehicles? The city is comparatively dense and has one of the top subways in the world. But what is most striking about its transformation is the increase in cycling and walking during this period – they increased from 55.4% in 2010 to 68% in 2020. Numerous programs offered by three levels of government explicitly prioritized bicycles over cars and reduced on-street car parking to make room for bike lanes. They taxed and restricted more polluting vehicles, and gradually phased them out, while providing a conversion bonus for the purchase or lease of electric-assisted bicycles and cargo bikes. In addition, car ads had to include messages promoting greener methods of transportation, and incentives were provided for bike repairs and tune-ups. Designated a Landmark case study by our sustainable transportation peer review and selection panel in 2022.

Opting Out in Germany for Non-Renewable Energy  

While many people in Germany say they would use green energy if presented with a choice, very few consumers do so. In contrast, most people have been using green energy in a few German municipalities where citizens have had to opt out for non-renewable energy supplies rather than having to opt-in to get renewable ones. This case study also illustrates the connection between green power choices and clean air / environmental health, and the value of randomized control trials (RCTs) for measuring program impacts. Designated a Landmark case study by our Building Energy peer review panel in 2022.

Carpooling and Vanpooling in San Mateo County, California  

This program promotes carpooling and vanpooling instead of driving alone during peak commute periods, using advertising (online, video, and display), challenges, and prize-based campaigns to attract and retain its target audience. It also made its standard Guaranteed Ride Home system easier to use. This case study illustrates the timing of incentives to promote habit formation. It also exemplifies how benefits can be increased by integrating some of the participant-facing aspects of multiple, independent programs in neighboring regions.

Virgin Atlantic’s Airline Captains Improve Fuel Efficiency  

Virgin Atlantic Airways (VAA) conducted an eight-month pilot in 2014 to test the potential roles and impacts of monitoring, performance information, personal targets, and prosocial incentives on the fuel-use behavior of their captains. All 335 of VAA’s captains were part of the pilot, and they were randomly assigned to four separate treatment groups. Since the pilot, the approach has become business as usual at VAA, and the technology was commercialized through Signol and updated to a web-app and email rather than post. Designated a Landmark case study in 2021.

Norway’s Promotion of Electric Vehicles  

Several policies / incentives, in place over an extended period, have made Norwegians more likely to purchase electric vehicles (EVs) than people in any other country. These incentives have included: exemption from vehicle registration and high purchase taxes, reduced road tolls, free parking, and access to some bus lanes. A similar long-term approach could be adapted for other big-ticket purchasing behaviors where the impact justifies the expense – for example energy-efficient home / building retrofits and appliances. Norway's electric cars are close to zero-emission as 98% of its electricity came from hydropower.

Seattle’s Just One Trip Phase II  

Just One Trip Phase II illustrates the use of Propensity Modelling / Predictive Analysis, Street Ambassadors, Quality Online User Experience (UX), and trip planning to reduce the proportion of single-occupant car trips in Seattle WA, USA. It engaged over 21,000 people and on average participants reduced four drive-alone trips per week per person. Designated a Landmark case study in 2020.

City of Austin’s Leave Time Travel Incentive  

The City of Austin reduced employee commute travel by one million vehicle miles within six months of making its Leave Time Reward (LTR) a permanent incentive. During this period, the percentage of drive-alone trips fell from 53% to 41%. Attribution of these impacts to the City’s time off incentive policy is strengthened because that policy was introduced in the pilot study, then withdrawn after the pilot, then later reintroduced for the permanent program (Reversal Design.) Designated a Landmark case study in 2020.

Stay on the Ground  

The most effective approach to-date at shifting air travel to train travel, and also at promoting the sale of carbon offsets for airplane travel, this approach could also work well for other behaviors that are perceived by the audience as clearly important to do, yet are not being adopted by many people.

Capitol Hill In Motion  

Capitol Hill In Motion is a recent evolution of the individualized marketing approach used by King County, Washington State, USA. It illustrates how to further engage communities where most trips are already not drive-alone. With remarkably high signup rates, this campaign also delivered a solid 16% average reduction in drive-alone trips (surpassing the campaign goal and King County’s overall goal of a 10% reduction).  Designated in 2017. 

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