Worldwide, some 83 million cars rolled off the assembly line in 2013. Of those new cars, 1.3 million contained an electric motor and battery, as well as an internal combustion engine—hybrid cars hardwired for better fuel economy and lower emissions.
Hybrid cars, such as the Toyota Prius, merge strengths. Gasoline- or diesel-powered engines excel at sustaining high speeds (highway driving) but have a harder time overcoming inertia to get moving (city driving). Electric motors are uniquely efficient at low speeds and going from stop to start. They also can:
- keep a car’s air-conditioning and accessories running while idling at a traffic light;
- capture the kinetic energy typically released as heat during braking and convert it back into electricity; and
- boost the engine’s performance, allowing it to be smaller and more efficient.
Hybridization has been called the vanguard of a revolution, catalyzing fuel efficiency and challenging the auto industry to innovate. But that is true only if they pave the way for full-electric vehicles—only motors and no engines at all—which can run solely on clean energy.
83 million cars [manufactured] in 2013: PwC. Autofacts Global Industry Outlook. London: PricewaterhouseCoopers, 2014.
“light duty” vehicles…emissions: EPA. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2012. Washington, D.C.: U.S. Environmental Protection Agency, 2014.
transportation sector’s…emissions: UNEP. Hybrid Electric Vehicles. Nairobi, Kenya: United Nations Environment Programme, 2009.
2013, 1.3 million…hybrid cars: IEA. Energy Technology Perspectives 2014. Paris: International Energy Agency, 2014.
fuel economy improvements: IEA. Technology Roadmap: Fuel Economy of Road Vehicles, Paris: International Energy Agency, 2012.
Lohner-Porsche Semper Vivus: Porsche. “Prof. Ferdinand Porsche Created the First Functional Hybrid Car.” Press release, Porsche Cars North America, New York, April 20, 2011.
fuel economy regulations: Körner, Alex, and Sheila Watson, eds. Fuel Economy State of the World. London: Global Fuel Economy Initiative, 2016.
petrol car’s energy consumption: U.S. Department of Energy. “Where the Energy Goes: Gasoline Vehicles.” https://www.fueleconomy.gov/feg/atv.shtml.
99 percent…is waste: Hawken, Paul, and Amory Lovins. Natural Capitalism: Creating the Next Industrial Revolution. New York: Little Brown, 1999.
battery costs declin[ing]: National Research Council. Cost, Effectiveness, and Deployment of Fuel Economy Technologies for Light-Duty Vehicles. Washington, D.C.: The National Academies Press, 2015.
price premium, but…reduced fuel costs: IEA, Fuel Economy.
vehicle miles traveled…rebound effect: Gillingham, K., M. Kotchen, D. Rapson, and G. Wagner. “The Re-bound Effect is Overplayed.” Nature 493 (2013); Linn, Joshua. The Rebound Effect for Passenger Vehicles. Washington, D.C.: Resources for the Future, 2013.
1 billion motor vehicles worldwide: Sperling, Daniel, and Deborah Gordon. Two Billion Cars: Driving Toward Sustainability. New York: Oxford University Press, 2009; Voelcker, John. “Two Billion Vehicles Projected to Be on Roads by 2035.” Christian Science Monitor. July 29, 2014.
By 2035…more than 2 billion: Voelcker, “Two Billion.”
Correction: Those additional 315 million cars can reduce carbon dioxide emissions by 4 gigatons by 2050, saving owners $1.76 trillion in fuel and operating costs over three decades.
Project Drawdown defines the cars solution as: the increased use of hybrid cars. This solution replaces the use of conventional internal combustion engine (ICE) cars.
Increasing the fuel efficiency of passenger vehicles is a key strategy to reduce fossil fuel use and greenhouse gas emissions associated with transportation. Fuel efficiency can be affected by many factors, including: vehicle technology and design, driver behavior, and road infrastructure. This study focuses on the hybridization of the drive train, which accounts for 25 percent of reduced fuel consumption in conventional gasoline engine cars – the largest impact available from a single technology (IEA, 2012). This work compares the potential financial and environmental impacts of a rapid global adoption of hybrid cars to a scenario in which adoption remains at its current level.
Hybrid electric vehicles supplement an internal combustion engine with at least one electric motor and a battery large enough to power the vehicle by generated electricity. They are distinct from electric vehicles which are powered, in part  or in whole, by grid electricity. Hybrid electric vehicles have greater fuel efficiency than ICE cars because they use stop-start technology, which reduces idle time, and regenerative braking, which recovers the energy that would otherwise be dissipated when brakes are applied.
Total Addressable Market 
The total addressable market for this technology is total urban and nonurban global passenger-kilometers, projected to 2050. Data from the International Energy Agency (IEA) and International Council on Clean Transportation (ICCT) is used to determine the urban segment common to all urban transportation solutions. Global adoption in 2014 was based on estimates of the fraction of light duty vehicles that are hybrid, and on average estimates of total light duty vehicle passenger-kilometers (IEA, 2012). Future adoption was calculated differently depending on the scenario.
Adoption Scenarios 
Impacts of increased adoption of cars from 2020-2050 were generated based on three growth scenarios, which were assessed in comparison to a Reference Scenario where the solution’s market share was fixed at the current levels.
- Plausible Scenario: Here, the average of collected conservative projections from several sources is used. It is also assumed that 50 percent of hybrid passenger-kilometers are urban each year.
- Drawdown Scenario: The average of two ambitious adoption prognostications is used.  It is assumed that average annual hybrid use increases by 50 percent by 2050,  and that 50 percent of hybrid passenger-kilometers are urban each year.
- Optimum Scenario: The adoption used in the Drawdown Scenario is taken. It is then assumed that average annual hybrid use increases by 100 percent by 2050 (increasing linearly from 100 percent in 2014 to 200 percent in 2050). This reduces the number of vehicle-kilometers per passenger-kilometer, fuel usage, and operating costs. 50 percent of hybrid passenger-kilometers are urban each year until 2031, when an annual 5 percent decline starts until it is 0 percent urban. This is due to assumptions made regarding adoption trajectories and integration with other solutions (see below).
Fuel emissions were based on the global average fuel economy, and indirect emissions from construction of the vehicles were included (hybrids were found to emit slightly more per vehicle).
Purchase costs for hybrids and ICE cars were estimated using price data for various car categories available in the USA, and were scaled using global price data from numbeo.com.  Although ICE car prices may change, no learning rate was assumed. For hybrid vehicles, a 3 percent learning rate was assumed based on estimates from peer-reviewed research.
Operating costs include fixed costs, such as insurance, as well as variable maintenance and fuel costs, which represent the main difference between the two technologies. The fuel costs were based on an average global fuel economy using 19 data points, and on the average fuel price over the 10 years prior to the base year, 2014.
Consistency with other solutions (such as electric vehicles) was maintained by using harmonized inputs for ICE car price, fuel economy, etc. The total adoption of hybrids is limited by the market from 2044 onwards, since hybrids were lowest in integration priority  of all the urban modes of transportation. The Optimum Scenario, therefore, resulted in no hybrid use in urban environments.
Between 2020 and 2050, the Plausible Scenario projects 315 million hybrids on the road, resulting in the reduction of 4 gigatons of carbon dioxide-equivalent emissions due to lower fuel consumption. This includes the increased indirect emissions associated with the production of hybrid vehicles. Operating costs are reduced by US$1.8 trillion as compared to a business-as-usual Reference Scenario. 
The Drawdown Scenario has 579 million hybrids on the road, and sees 11 gigatons of emissions avoided. Finally, the Optimum Scenario sees 440 million hybrids reducing 15.7 gigatons of emissions. The number of hybrids in the Optimum Scenario is reduced compared to previous scenarios because: 1) a higher car occupancy is assumed in this scenario; and 2) the adoption is constrained as a result of the aggressive adoption of electric vehicles in this scenario.
With the understanding that gasoline-powered cars will not disappear immediately, hybrid electric vehicles can be a good mid-term solution for mitigating transportation emissions, as their price differential with ICE vehicles is not large but their development can help electric vehicle technology grow. Hybrids can take market share from ICE cars while potential zero-carbon transport methods, such as electric vehicles that run entirely on battery power, continue to improve. This may require increased investment to reduce the premium over ICE cars, and/or subsidies to attract demand. There might be improvements in internal combustion engine technology that reduce the impacts calculated. From a societal perspective, replacing ICE cars with hybrids results in lower greenhouse gas and other air pollutant emissions associated with adverse health effects.
 Plug-in hybrids are included in the electric vehicle model.
 For more on the Total Addressable Market for the Transport Sector, click the Sector Summary: Transport link below.
 For more on Project Drawdown’s three growth scenarios, click the Scenarios link below. For information on Transport Sector-specific scenarios, click the Sector Summary: Transport link.
 Based on the IEA 2°C Scenario (2016) and the World Energy Council's 2011 projections of sales/stock, with ICCT 2012 Global Roadmap Model estimates of usage.
 This corresponds to a behavioral change in private car use, supported by the current positive trends in ride-sharing growth and potential future restrictions in car usage in cities to encourage mode shift.
 A website where several thousand data-points have already been collected for several countries.
 For more on Project Drawdown’s Transport Sector integration model, click the Sector Summary: Transport link below.
 The 7 urban Project Drawdown solutions were prioritized by energy efficiency and space efficiency, so non-motorized modes like walking and bike infrastructure were highest and hybrids wound up last, since they were the least efficient of all considered options under typical usage assumptions.
 All monetary values are presented in US2014$.