Many cars in a traffic circle in Mexico City, Mexio.
Technical Summary

Carpooling

Project Drawdown defines the carpooling solution as increasing urban car occupancy worldwide. This solution replaces the urban conventional practice of using single-occupancy vehicles.

Car occupancy is a key metric for efficient use of cars. Cars are very space intensive in that they are a key cause of congestion in cities. Efficiencies of car use can approach that of buses if enough people share cars for the same trips. This we call carpooling, and interpret it for all urban car trips. Carpooling is often mainly associated with commuting in North America, but there is much potential for it to reduce emissions worldwide for a variety of trip purposes. Implementing or stimulating carpooling includes use of high occupancy-vehicle (HOV) and high occupancy-tolling (HOT) lanes, HOV priority parking, shared taxis, and shared ride hailing (Uber, Lyft, etc.). Ride-hailing systems often are used as single user taxis, which doesn’t increase car occupancy; however the shared version of these services (UberPOOL, Lyft Shared Rides, etc.) can increase occupancy if well implemented, and is considered carpooling in this analysis.

Methodology

In this study, carpooling trips are compared with single-occupancy car trips. A fully adopted carpooling trip is considered as three passengers sharing a trip[1]. We therefore assume that each car trip either has one or three passengers for the purpose of modeling. Data on car mode share and average car occupancy are used to estimate urban vehicle trips worldwide. Global car occupancy is estimated at 1.57 persons per trip,[2] which would indicate 29 percent current adoption[3] of carpooling as defined. Changes to car occupancy are assumed to result from the approaches listed above implemented worldwide by policymakers, alongside a cultural shift that embraces sharing of trips and that is partly supported by technology that reduces the stigma and perceived safety issues. Increased occupancy targets for 2050 are set with annual increases from the current value and, each year, the average occupancy is used to estimate the number of trips that have fully adopted carpooling compared with those that are single occupancy.

Total Addressable Market

The total addressable market for carpooling is estimated as the total passenger-kilometers of urban travel globally after the non-car solutions have been adopted (that is, the estimated car-only urban mobility worldwide). Note that this declines in more aggressive scenarios as more sustainable modes like public transit take more mode share.

Adoption Scenarios

Impacts of increased adoption of carpooling from 2020 to 2050 were generated based on two growth scenarios. These were assessed in comparison with a Reference Scenario, in which the solution’s mode share was fixed at the current percent levels. In each scenario, an adopted carpooling trip is defined as one with  three people sharing the trip.

  • Scenario 1: This scenario projects that the global average car occupancy will be 1.75 in 2050, and hence will grow linearly from 1.57 to that value.
  • Scenario 2: This scenario projects that the global average car occupancy will be 2.0 in 2050, and hence will grow linearly from 1.57 to that value.

Financial Model

As carpooling is defined here, there are no first costs to adopting the practice. However, an operating cost difference is included: with fewer cars on the road, the maintenance and fuel (and for EV’s, electricity) costs per passenger-kilometer are reduced, as they are assumed constant per vehicle-kilometer driven.[4] The average single occupancy vehicle operating cost is divided by the car occupancy, which represents a 67 percent drop (from costs per single occupancy traveler to costs per three carpooling travelers). The price of fuel is the average of data from 2007 to 2018 and comes from International Energy Agency (IEA) Energy Prices data. The electricity grid prices come from over 500 data points from several countries over 10 years.

Integration

As mentioned earlier, the carpooling total addressable market only considers the urban mobility after all more sustainable solutions are adopted (walking, biking, public transit), so the mobility markets are shared among all these solutions. A major element of integration here is how the other car solutions (electric cars, hybrid cars) interact with the carpooling solution. As electric vehicle (EV) adoption increases, the effect of carpooling[5] is reduced since EVs are more efficient than internal combustion engine vehicles. More specifically, the energy type shifts increasingly from gasoline to electricity. Similarly, as carpooling adoption increases, the average car occupancy of EVs increases, leading to a reduced impact of electric cars. Similar logic applies to hybrid cars as they relate to carpooling. These have been taken into account. In addition, it was ensured that the same car inputs were used across relevant Transport Sector models (emissions factors, fuel economy, etc.).

Results

Scenario 1 results in a total reduction of 7.7 gigatons of carbon dioxide-equivalent greenhouse gases, and operating savings of US$5.2 trillion.[6] Scenario 2 shows a reduction of 4.2 gigatons of emissions and US$2.6 trillion in car operating costs for consumers, which are lower since the total car mobility is lower due to more use of walking, biking, and public transit. To put these results another way: a three-person family always driving together instead of using their three family cars individually would save more than 3.2 metric tons of carbon dioxide, and over US$2,000, in a year[7].

Discussion

The financial costs of travel are motivators for carpooling, but history shows that increased carpooling in North America is driven most forcefully by external forces rather than by policies designed to promote carpooling. Carpooling for commuting has declined from highs of 30 percent in the US to under 10 percent, but some recently introduced services may help stimulate growth.[8] In North America and Europe, there is still a stigma attached to sharing rides with strangers. Shared ride hailing only accounts for less than one fifth of ride-hailing services, partly due to the added inconvenience, but also to perceived safety risks. Uber announced that almost 6,000 sexual assaults and 107 deaths were reported on its services for 2017 and 2018. This remains an important concern for many, but Uber’s report also noted that the rate of sexual assault and fatality is lower than the US national average.[9]

On the contrary, carpooling has been popular in developing word countries for financial reasons. In many countries in Africa, Latin America, and the Caribbean, the sharing of taxis (“bush taxis,” “route taxis,” “taxis collectifs,” or “carros públicos”) on special, often fixed or semi-fixed, routes for short or longer distance journeys has been around for decades and has been popular since it helps reduce costs for travelers and allows drivers to adapt to market demand.[10] However, with rising incomes, car ownership has been rising worldwide, and this is likely to lead to lower pooling of rides. Around 80 million cars are sold annually, and an increasing share of them are sport utility vehicles (SUVs), which consume more fuel than smaller vehicles. China is already the world’s largest car market, with India, Mexico, and Brazil being other large buyers. Overall, the world is moving away from, rather than toward, carpooling and shared rides for urban mobility.

There is hope, however, because of the availability of appropriate urban policy, a growing acceptance of sharing trips by younger travelers partly for environmental reasons, a growing movement for Mobility as a Service (MaaS), as well as the projections from the scientific community of the critical need for shared mobility to avoid gridlock in an era with self-driving cars. All of these are strong drivers that will help grow carpooling.


[1] We exclude a nonpassenger driver from that calculation.

[2] ICCT (2012) Global Roadmap Model v1.0, www.theicct.org, accessed 1 September, 2017.

[3] Current adoption is defined as the amount of functional demand supplied by the solution in 2018. This study uses 2014 as the base year.

[4]  An additional person weighing 75 kilograms in a typical 1800-kilogram car increases the total weight transported by less than 4 percent, so wear and tear and fuel usage do not change much with more people.

[5] Carpooling is assumed independent of car type (internal combustion engine, EV, hybrid, etc.)

[6] All monetary values are presented in 2014 US$.

[7] We assume here that each car would be driven 15,700 km (9,700 miles) per year, and include maintenance, fuel, and electricity.

[8] McKenzie, B. (2015). Who drives to work? Commuting by automobile in the United States: 2013 (American Community Survey Reports No. ACS-32) (p. 28). US Census Bureau. Retrieved from https://www.census.gov/library/publications/2015/acs/acs-32.html

[9] Vittert (2019). Uber’s data revealed nearly 6,000 sexual assaults. Does that mean it’s not safe? http://theconversation.com/ubers-data-revealed-nearly-6-000-sexual-assaults-does-that-mean-its-not-safe-128689

[10] Powers (2015). What Trinidad could teach Uber and Lyft, https://www.ozy.com/opinion/what-trinidad-could-teach-uber-and-lyft/60356/