Technical Summary

Hybrid Cars

Project Drawdown defines the hybrid cars solution as the increased use of hybrid cars (not plug-in hybrids). 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 over 40 percent of the improvement potential in conventional gasoline car fuel consumption – the largest impact available from a single technology[1]. 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[2] 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[3]

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) are used to determine the urban segment common to all urban transportation solutions. Global adoption in 2018 was based on estimates of the historical and projected fractions of light duty vehicles that are hybrid, and on average estimates of total light duty vehicle passenger-kilometers[4]. Future adoption was calculated differently depending on the scenario.

Adoption Scenarios[5]

Impacts of increased adoption of cars from 2020 to 2050 were generated based on two growth scenarios, which were assessed in comparison to a Reference Scenario where the solution’s market share was fixed at the current levels.

  • Scenario 1: 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.
  • Scenario 2: An assumption of a transition to EVs is used where hybrid adoption first grows according to the IEA 2DS scenario until the late 2040s, when adoption declines. Also, 50 percent of hybrid passenger-kilometers are urban each year until 2030 when it declines.

Emissions Model

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).

Financial Model

Purchase costs for hybrids and ICE cars were estimated using price data available in the USA, EU, and Japan, as well as global weighted averages. Although car prices may change, no learning rate was assumed for ICE’s or hybrid vehicles.

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 2007–2018.


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, since hybrids were lowest in integration priority[7] of all the urban solution modes due to its high energy, emissions and space requirements. The Optimum Scenario, therefore, resulted in lower hybrid use in urban environments compared to other scenarios. Additionally, as the hybrids were integrated with the Carpooling solution, over time, increased occupancy of hybrids was assumed over time as the Carpooling solution adoption increased. This changed the fuel consumption variables.


In 2050, Scenario 1 projects 621 million hybrids on the road, resulting in the reduction of 7.9 gigatons of carbon dioxide-equivalent emissions due to lower fuel consumption (over 2020–2050). This includes the increased indirect emissions associated with the production of hybrid vehicles. Lifetime operating costs[8] are reduced by US$6 trillion[9] compared with a business-as-usual Reference Scenario for an increased purchase costs of US$3.6 trillion.

Scenario 2 has 236 million hybrids on the road in 2050, and sees 4.6 gigatons of emissions avoided (both lower than the Plausible due to a transitioning to EVs).


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 as large as EVs but their development can help electric vehicle technology grow (as batteries get better). 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. There are some challenges with hybrid adoption however, since the vast majority of sales happen in Japan led by Toyota (including its best-selling model, the Prius). Our data show that from 1999-2017, 59% of Hybrid sales were in Japan. The growth of HEV adoption is therefore currently dependent on Japan but Japan represents only 4-5 million out of over 80 million annual passenger vehicles sold. With current global HEV stocks estimated to be 15-16 million, there is much room to grow. Other major markets such as China and the US would need to complement their EV-support policies with HEV-support policies to help encourage adoption. These countries seem to be focused on the EV market however.

Note: August 2021 corrections appear in boldface.

[1] International Energy Agency. (2012). Technology Roadmap: Fuel Economy of Road Vehicles. Paris.

[2] Plug-in hybrids are included in the electric vehicle model.

[3] For more on the Total Addressable Market for the Transport Sector, click the Sector Summary: Transport link below.

[4] Institute for Transportation & Development Policy, & UC Davis. (2014, November). A Global High Shift Scenario. Institute for Transportation & Development Policy, University of California Davis. Retrieved from

[5] For more on Project Drawdown’s growth scenarios, click the Scenarios link below. For information on Transport Sector-specific scenarios, click the Sector Summary: Transport link.

[6] For more on Project Drawdown’s Transport Sector integration model, click the Sector Summary: Transport link below.

[7] 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.

[8] The net operating savings for the full lifetime of all units installed during 2020-2050.

[9] All monetary values are presented in US2014$.