Light rail vehicle in Krakow, Poland
Technical Summary

Public Transit

Project Drawdown defines the public transit solution as: the increased usage of mass transit or public transport to get around cities. This solution replaces the use of conventional internal combustion engine (ICE) cars.

Public transit  is a collection of different urban passenger transport modes (e.g. metro, bus, tram, ferries), which can facilitate the mobility of large numbers of people. It has long been a structural part of urban environments worldwide, and while its market share has decreased through the second half of the 20th century, it remains the only viable alternative to travel by private car on many occasions. As the population of urban areas is expected to grow from 2020-2050, public transit  can claim an important share of the new travel demand. The increased usage of public transportation reduces the need to drive cars as a form of urban mobility.


Using information from studies and reports conducted by major international institutions, several possible outcomes of various aggressive adoption scenarios were examined.

Total Addressable Market[1]

The total addressable market for public transit is defined as the total urban mobility, in passenger-kilometers, projected by institutions such as the International Energy Agency (IEA), the International Council on Clean Transportation (ICCT), and collaborative work between the Institute for Transportation and Development Policy and the University of California–Davis (ITDP/UCD). Current global adoption[2] of public transit, excluding non-motorized trips, is 34 percent of the market, boosted mainly by high adoption rates in low-income countries where car ownership is lower. In high-income areas like Europe and Japan, public transit already has significant and rising adoption; still, conventional ICE vehicles own the largest part of the market share in Europe and North America, as well as in other developed regions. Meanwhile, the adoption of public transit  in Asia and Africa is threatened by a combination of economic growth and poor transit infrastructure, partly leading to a low business-as-usual projection of global public transit  adoption in 2050 as urban mobility expands rapidly through the use of other modes especially private cars.

Adoption Scenarios[3]

Impacts of increased adoption of public transit  from 2020-2050 were generated based on two growth scenarios, which were assessed in comparison to a Reference Scenario where the solution’s usage follows a case close to business as usual (the IEA Reference Technology Scenario - RTS).[4] Future high growth projections of public transit  are aligned with the IEA and ITDP/UCD.

  • Scenario 1: Estimates of future growth were based on projections of public transit  adoption from the 2016 IEA 2°C Scenario, where adoption reaches 22 percent in 2050.
  • Scenario 2: Projections were aligned with the ITDP/UCD 2014 Global High Shift Scenario, where adoption reaches 35 percent in 2050.

Emissions Model

Emissions calculations capture electricity, fuel use, black carbon, and indirect emissions for public transit, all weighted according to the public transit mode. Electricity and fuel data were obtained from ITDP/UCD and other sources. Car emissions are based on fuel use and black carbon alone. Fuel economy data is taken from multiple sources and represents the global car fleet.

Financial Model

The financial analysis is conducted from the perspective of the user, rather than public transit  operators, municipalities, or society as a whole. This is valuable so that those making decisions about whether to travel by public transit  or by conventional vehicles have a better idea of the financial and emissions aspects of that decision. Public transit  first costs have been excluded from this model to prevent misinterpretation of the cost of implementation, but car first costs have been included as a fixed operating cost of depreciation. By contrasting the use of public transit  with internal combustion engine vehicles, the depreciated costs of owning and using a car are compared to the cost of purchasing a public transit  ticket. The financial evaluation is thus based on the net operating costs: the weighted average ticket price of public transit  options by region,[5] compared to the fixed operating costs (that is insurance and depreciation), fuel costs, and other variable operating costs (e.g. maintenance) of car ownership.

To ensure that this model was well integrated with other Drawdown models, we used the common market and car inputs across all relevant solutions. Adoption was also restricted so as to not exceed the total mobility demand represented by the total addressable market.


The Scenario 1 results in an emissions reduction of 7.5 gigatons of carbon dioxide-equivalent greenhouse gases and over US$2 trillion[6] in lifetime operations savings, with adoption going to 22 percent in 2050. In the Scenario 2, emission reductions could reach as high as 23 gigatons.


When combined with other technologies and approaches such as electric/hybrid engines, clean energy production, vehicle automation, and car sharing, the impact of public transit  can increase significantly. Without public transit -focused investments and policy, it is likely that much of the projected growth in urban mobility would be taken up by private cars, and even if exciting developments like electric, autonomous, shared-car fleets become widespread, public transit would be needed on high-demand routes. There therefore needs to be a significant effort to ensure that public transit  systems are attractive means of mobility for the increasingly urbanized world. We excluded public transit  investment costs for governments, but we also excluded additional benefits of increased public transit  usage such as reduced congestion from private vehicles, and potentially more city space reclaimed from parking lots that are not required. It is unlikely that adding these elements would alter the basic conclusion that public transit  is a key part of reducing urban transport emissions.


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

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

[3] 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.

[4] This assumption is contrary to the standard Project Drawdown Reference Scenario, which assumes that growth occurs in relation to the overall growth of the market, with the percent adoption remaining fixed at current year levels. Given current trends, this assumption is considered to be too optimistic without strong policy in countries such as China and India where growth in conventional car ownership is on the rise.

[5] Ticket data came from, and has been averaged by Drawdown Region.

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