How Does Your Car’s Emissions Compare to Transit?

How Does Your Car’s Emissions Compare to Transit?

Today there is a common conception, or perhaps misconception, that transit is greener than traveling by car – meaning that it produces lower emissions. For many, there is a guilt associated with the convenience of car travel – they presume it generates more emissions –  but the reality is illuminating and in some cases welcome.

Understanding the reality is vital so that we don’t implement expensive plans in the hopes of fighting climate change, when the actual impact is not cost-effective.

Compare Your Car’s Emissions to Transit (Google Docs Spreadsheet)

This Google Docs spreadsheet which anyone can access via a web browser helps show how your current car, or more relevantly – how the car you might be driving in 2025-2035 – emits CO2.

Timeframe is an Important Factor for Transit Projects

When considering major transit projects the emissions of cars being driven today are not as important as what the emissions will be of cars in the future. The Whitehouse announced in 2012 that the US DOT and EPA have issued standards that the average new US car (US fleet) must achieve 54.5mpg by 2025.

Transit projects such a “fixed guide rail” (e.g. commuter rail, heavy rail such as the SMART train and streetcars or trolleys) must be compared against car emissions at the midpoint of their lifespan. So if a train or trolley line takes 4 years to build, and  locomotives have a lifespan of 30 years, we should be comparing emissions to the average car in the year 2033.

Important Considerations for Transit Figures

It is also vital to understand key context around transit passenger mpg figures:

  • Transit Emissions Are Static Compared to Cars Which are Rapidly Improving
    Car and light truck emissions have rapidly improved not only because of legislation but also the powerful market force of consumers aware of the importance of mpg to save on their gas bill and fight climate change.Even looking over a long period of the last 15 years transit emissions have remained relatively static.

  • Adding Transit Has Diminishing Returns
    Transit achieves the highest passenger miles per gallon figures, and lowest emissions figures when trains and buses are at full capacity. Typically transit already serves the highest demand arterial routes such as east coast commuter trains serving major employment centers in New York City and Boston. Adding transit to less used corridors in suburban areas (E.g. Marin), or adding life-line buses that are not filled to near capacity serves to reduce passenger miles per gallon and increase emissions.

What Does this Mean?

This means we should not become over-fixated on transit as a means of fighting climate change. We need to look beyond the term “sustainability” and conduct accurate and realistic assessments.

It also means that we need to understand that switching people from driving cars to taking transit to has only a marginal effect at best  - and this effect is diminishing and becoming the reverse – cars are becoming cleaner than transit. This means that we need should be careful not to undertake programs that are extremely expensive (such as the $92 billion Plan Bay Area) or that make major impositions and result in adverse impact – such as adding high density housing near transit hubs, and disregarding impact on vehicle delays at highway intersections – as advocated by the draft California Governor’s Office of Planning and Research proposed new guidelines.

Plan Bay Area – Presumes 25.03mpg by 2040 When 54.05mpg is Mandated by 2025

The $92 billion Plan Bay Area assumes that for the year 2040 the on-road vehicle fleet fuel economy will be only 25.03 mpg, in stark contradiction to the US DOT and EPA have issued standards that the average new US car (US fleet) must achieve 54.5mpg by 2025.  (Source: Plan Bay Area Draft Environmental Impact Report, page 406). Plan Bay Area states:

“Based on data provided by MTC, this energy analysis uses an average on-road vehicle fleet fuel economy
of 17.94 mpg for the baseline (2010) year and 25.03 mpg for 2040.2″

Plan Bay Area’s flawed assumptions are further exposed by EPA reported average mpg figures for new vehicles for the 2012 reporting year of 23.6mpg, an increase of 1.2mpg over the previous reporting year. (Source: LA Times).

Deadhead Miles and Weight

Major reasons for transit’s high energy usage and emissions stem from dead head miles and weight:

  • Dead head miles: When you drive from your home to the shops or work you drive directly from A to B. But a bus or train has to be positioned at the start of the route. For single track railway lines such as SMART this can be particularly inefficient. During these dead head miles no passengers are travelling anywhere, yet the energy of a bus is getting anything from 2mpg to 5mpg (e.g. for a modern hybrid bus)
  • Weight: Trains in the United States are heavy. This is due to the design philosophy of US trains which is quite different to European trains. In Europe trains are considerably lighter as the entire system is designed for collision avoidance.  In the US trains are instead designed for collision survival – so that if they are running on the same lines as freight (like SMART) they are defined as “heavy rail” and minimize loss of life should a collision occur. So even if steel wheels on rails reduce friction, the added weight for collision survival serves to counter this.

High Density Housing Near Transit Can Increase Delays and Emissions

Such new planning standards that disregard how new development can increase traffic congestion can be highly counter-productive. Instead of driving efforts in a way that in suburban areas can be the most effective – facilitating lower emissions by continuing to consider car delays – new high density housing built at traffic choke-points can make congestion far more acute. Cars that are avoidably stopped for longer can needlessly add to emissions – and this planning approach disregards the inconvenienced caused to the majority of travelers. For these reasons very careful consideration must be given to transit-oriented development in suburban areas.


The most important thing is that residents and decision makers – including mayors, councilors,supervisors, planning commissioners, planners and citizen advisory committee members – are aware of these facts. Because if we carry on down a path of presuming any transit is superior to cars and light trucks – we may end doing the opposite of what we intend – fighting climate change.