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New Comprehensive Lifecycle Energy and Emissions Inventory Includes Non-Operational Components; Large Aircraft Can Perform Better than Light Rail

Energy consumption and GHG emissions per PKT (passenger kilometer travelled). The vehicle operation components are shown with gray patterns. Other vehicle components are shown in shades of blue. Infrastructure components are shown in shades of red and orange. The fuel production component is shown in green. All components appear in the order they are shown in the legend.). Chester and Horvath (2009). Click to enlarge.

A new comprehensive lifecycle energy, greenhouse gas emissions, and selected criteria air pollutant emissions inventory by researchers at the University of California, Berkeley that includes vehicles, infrastructure, fuel production, and supply chains found that find that total life-cycle energy inputs and greenhouse gas emissions contribute an additional 63% for onroad, 155% for rail, and 31% for air systems over vehicle tailpipe operation.

Inventorying criteria air pollutants showed that vehicle non-operational components often dominate total emissions. Life-cycle criteria air pollutant emissions are between 1.1 and 800 times larger than vehicle operation. Ranges in passenger occupancy can easily change the relative performance of modes, with large aircraft performing better than light rail in some of the areas investigated. The study was published 8 June in the open access IOP journal Environmental Research Letters.

In order to effectively mitigate environmental impacts from transportation modes, life-cycle environmental performance should be considered including both the direct and indirect processes and services required to operate the vehicle. This includes raw materials extraction, manufacturing, construction, operation, maintenance, and end of life of vehicles, infrastructure, and fuels. Decisions should not be made based on partial data acting as indicators for whole system performance.

—Chester and Horvath (2009)

Mikhail Chester and Arpad Horvath inventoried on-road, rail, and air travel to determine energy consumption, greenhouse gas (GHG) emissions, and criteria air pollutant (CAP) emissions (excluding PM, lead, and ozone due to lack of data). The onroad systems include three automobiles—(2005 Toyota Camry), SUV (2005 Chevrolet Trailblazer), and pickup (2005 Ford F-150) to represent the range in the US automobile fleet and critical performance—and two urban buses with off-peak and peak passenger loadings.

83% of rail passenger kilometers are performed by metropolitan systems (with Amtrak serving the remaining). The researchers chose heavy rail electric metro, heavy rail diesel commuter transit, and light rail transit (LRT) to capture the gamut of physical size, fuel input, and service niche. Metro and commuter rail were modeled after the San Francisco Bay Area’s (SFBA) Bay Area Rapid Transit and Caltrain while the LRT modes are modeled after San Francisco’s (SF) Muni Metro and the Boston Green Line.

They evaluated small (Embraer 145), midsize (Boeing 737) and large (Boeing 747) aircraft to represent the range of impacts from aircraft sizes, passenger occupancy, and short to long haul segment performance.

US average data was used for all onroad and air mode components; particular geographic operating conditions was not captured. For each component in the mode’s life cycle, they calculated environmental performance and then normalized it per passenger-kilometer-traveled (PKT).

In the paper, the team reported the performance for modal average occupancy per-PKT.

Samples of the findings include:

  • Off-peak urban diesel buses has the largest energy consumption and GHG emissions per PKT, followed by the three light-duty vehicles. Peak urban diesel buses showed the best overall energy consumption and GHG emissions per PKT.
  • Of the non-road modes (rail and air), light aircraft showed the worst performance per PKT.
  • While in terms of fuel consumption large aircraft exceed the energy consumption of the rail modes, when all elements are factored in, that total consumption in MJ/PKT is lower than that of SF Muni light rail.
  • In terms of GHG emissions, large aircraft on a total g CO2e/PKT basis outperforms Boston light rail (the Green Line).
  • In terms of sulfur dioxide emissions, Boston light rail was by far the worst performer, followed by SF Muni.
  • For NOx, off-peak urban diesels were the worst performer, followed by light-duty vehicles and commuter rail.
  • For CO, the pickup truck was the worst performer, followed by the off-peak bus.

In general, they found that the dominant contributions to energy consumption and GHG emissions for onroad and air modes are from operational components, suggesting that technological advancements to improve fuel economy and switches to lower fossil carbon fuels are the most effective for improving environmental performance.

However, they found that rail’s energy consumption and GHG emissions are more strongly influenced by non-operational components than onroad and air and concluded that while energy efficiency improvements are still warranted coupled with lower fossil carbon fuels in electricity generation, reductions in station construction energy use and infrastructure operation could have notable effects.

Reduction in concrete use or switching to lower energy input and GHG-intensity materials would improve infrastructure construction performance while reduced electricity consumption and cleaner fuels for electricity generation would improve infrastructure operation for rail, they noted. Utilizing higher percentages of electricity from hydro and other renewable sources for rail operations could result in significant GHG reductions over fossil-based inputs such as coal.

This study creates a framework for comprehensive environmental inventorying of several modes and future assessment of non-conventional fuels and vehicles can follow this methodology in creating technology-specific results.

Future work should also focus on environmental effects not quantified herein, such as the use of water, generation of waste water, and toxic emissions. Detailed assessments of the end-of-life fate of vehicles, motor oil and infrastructure should also be factored into decisions. Through the use of life-cycle environmental assessments, energy and emission reduction decision-making can benefit from the identified interdependencies among processes, services, and products. The use of comprehensive strategies that acknowledge these connections are likely to have a greater impact than strategies that target individual components.

—Chester and Horvath


  • Mikhail V Chester and Arpad Horvath (2009) Environmental assessment of passenger transportation should include infrastructure and supply chains. Environ. Res. Lett. 4 024008 doi: 10.1088/1748-9326/4/2/024008



Rather perverse to compare light rail to air, no? For the most part, they serve radically different markets.


Surprising results.
Autos and SUVs serve quite different markets also.
Light rail cars only appear green, when they travel empty.


It would be interesting to see the difference between peek and off-peek rail systems as well. I would guess the result would be similar to the urban bus figure. Am I missing something but wouldn't it make sense to operate much smaller mini-buses (or fewer train cars) during off-peak times? Yes this would require an innitial greater cost in buying more vehicles (for bus lines) and storage space for the unused RR cars and buses, but energy cost savings might more than make up for it. Sometimes we don't need to wait for that technological wind-fall to solve our problems. We might have the answer already.


I have no access to the report, so I am afraid I have only questions and opinions on offer.

The infrastructure component for rail is big. How much that is per passenger km is dependent on how long the infrastructure is going to last. Many British railway lines are more than a century old. So what were their assumptions?

What is 'infrastructure operation'? That is a big component, but what is it? Station heating/cooling, lighting, opening and closing bridges? The infrastructure operation component for roads is much smaller. Did they include public lighting of roads? Where does all that energy go for operating a railway line?

I find the vehicle inactive operation a big component. Since many trains are in operation round the clock, or at least 50% of the time, it would seem that they assumed a standing train consumes more than a moving train.

What was the grid mix for electric trains?

Why did they leave out high speed rail? That would have been an interesting comparison to aviation. A missed opportunity.

But: kudos to Berkeley for having used SI units!


Anne it's all from a US perspective so isn't applicable to the rest of the world.

I think the off peak bus thing is a big red herring. Buses and trains need to offer a regular service throughout the day in order to be usable.

There are plenty of aircraft that fly at low load factors (or even empty in the case of repositioning or slot-maintaining sectors). Sometimes they fly full too - kind of like buses!

The only meaningful way to look at it is to compare the average emissions over a year for all modes so it's a bit odd to single out buses like that.


There is a problem with the selection of the Green Line in Boston being used as typical light rail. The Green Line, being the oldest American line still in existence, usually carries only 2 cars per train, a very atypical and inefficient number. It also makes all of its many stops over very small distances. The energy for all this stopping and starting is not typical of any other light rail line in Boston. The others all have close to a dozen cars per train, and stop far less often over much larger distances. This seems to have been a very poor choice, and must skew the results, causing significant errors in the conclusions.


Are you sure it's just a "poor choice?" Maybe it's a deliberate attempt to skew the results.


One thing to take from the report is that different modes of transport have their role in serving different needs and in some ways can complement strategies for reducing the energy intensity of transport.

Surely the most energy efficient mode of transport is two feet and pedal power, and there is much potential for people to walk and cycle more, for energy, carbon and health benefits, since many journeys are less than two miles. I go further than this and regularly walk 4 miles to work.

The next step up is public transport, light rail and urban rail commuting – modes which are very efficient in urban situations at peak times. However, it is clear that buses used off peak has a massive impact on energy use and carbon intensity. Predictably the UK’s response has been ‘must get more people on buses’. There is some potential, if routes, frequency and choice of fleet is planned carefully at best to mitigate some of the lack of efficiency peak periods. However, it is time to accept the reality, against the thrust of environmental and sustainable transport groups, that the car does have a role and without it, getting a truly integrated transport system will not happen.

Unfortunately the lack of data on diesel or electric fuelled rail travel does not allow us to compare this mode to air travel or long distance road travel. Given the massive subsidies required for rail to serve non-commercial (i.e. not used very much) services and for wider operation costs, this suggests to me that it is more carbon intensive than people think, especially if we factor in people getting taxi rides to the station, being dropped off and picked up and so on. Then there’s maintenance requiring fleets of vans etc etc.

I am glad to see that the findings of this study points towards a move away from oversimplistic sweeping statements that public transport = good and car = bad. Is it time to get placards out and protest in the streets about the energy consumption and carbon intensity of buses at off peak times? No. This is because people will still need to use off peak buses as much as people need cars. Therefore, it’s now time to move from public transport vs the car, rail vs air and so on to modes working together to do the jobs that they are best at.

In the meantime lets work also on a more sustainable energy mix that will support all of these forms – biofuels, electric etc. Again this call fro a move from the similar electric vs biofuels squabbling.


It is obvious even to the most casual observer that the commentators to this report have a bias toward light rail.

They simply can't stand that air travel might have an advantage over their favorite mode of transportation which they want to force everyone else to adopt.


"the commentators to this report have a bias toward light rail.

They simply can't stand that air travel might have an advantage over their favorite mode of transportation which they want to force everyone else to adopt."

You're joking right? The real problem is this report was comparing apples to oranges. Air travel is great - for distances of 500 miles or more[intercity] but for intracity travel lightrail is the way to go.


Well some of the comments do show that some really didn't even look at the graphs.

Public transportation systems clearly outperformed private cars and air travel in the majority of cases. It was only in energy efficieny that SF Muni LR was outperformed by large aircraft and in terms of CO2, large and mid sized aircraft outperformed the Boston Green line LR.

Some the the newer light rail systems, which i have no idea if they are listed in the graphs, have regenerative breaking system to make them even more efficient. The energy portion of the graphs don't really make sense if the boston system is more efficient than the SF one, given some comments about the green line, unless the composition is totally different. I do know that the Boston public transport system as a whole is one of the better funded ones but in this case I have no idea of how it is set up or what the study looked at.

The caveates in the study are things like the use of peak and non-peak for buses which must share infrastructure costs with cars (or may even increase them) to the not using similar catagories for the other systems. Since the hard costs are amortized over the distanced travelled by the users, the larger infrastructure costs for some are significantly lower because it's shared among many users.

As to some comments of the rail systems. Well commuter rail system go from city centers to other city centers. This is highly advantageous considering where airports are generally located.

And this is a largely US study. Using US energy production figures clearly skews the numbers for LRT systems since such a large portion of US electricity is from coal. In other juridictions, GHG gases would be down, at least in the operation of the system and the maintenance of the buildings.


"And this is a largely US study. Using US energy production figures clearly skews the numbers for LRT systems since such a large portion of US electricity is from coal. In other juridictions, GHG gases would be down, at least in the operation of the system and the maintenance of the buildings."

You're right about that: I wonder what the conclusions would have been if they had studied the Calgary C-train. Calgary's LRT is powered by wind energy.

OTOH it may be about the only thing in Alberta that is powered by the wind; 76% of their electricity comes from coal and 20% comes from NG. BTW our PM is from Alberta - explains a lot doesn't it.

fred schumacher

Present conditions may not be a very good indicator for the future. The achilles heel of air travel is that it requires energy dense portable fuel, namely, jet fuel, a type of kerosene. Although the military are investigating use of biofuels for aircraft, biofuel production has shown itself to be more problematic than first realized.

Rail, a form of linear transport, has the advantage of being able to be driven from mains electric power. Although electricity production presently is very dependent on fossil fuels, it does not need to be so. Electricity is the easiest form of energy to produce sustainably from non-carbon sources.

Roger Pham

There is no question that high-occupancy light rail and buses are much more energy-efficient than any other forms of transportation. Lower occupancy rate during off-peak traffic hours can be mitigated by using smaller vehicles or less-frequent trips.

But the most important issue NOT discussed here is that the heavy use of public transportation will alleviate traffic congestion of private autos. These autos have their engine idling for the most part, and spewing greenhouse gases and pollutants into the local air, thus greatly degrading fuel efficiency and urban air quality .


I see nowhere the mention of infrastructure costs for airplanes. Not to include the energy expenditure of building and maintaining airports grossly skews the results. In Seattle they have just completed construction of a 3rd runway, CO2 cost is estimated to be 4.7 million metric tons of CO2. And that is not even for a new airport, that is for an existing one. To include the infrastructure cost for one mode of transportation (light rail) and leave it out for another (aircraft) is highly biased and suspect.

Calvin Brock

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