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An Efficiency Breakdown: Travel Energy Usage

National efforts for efficiency and conservation continue to lead us to analyze aspects of daily life to find opportunities ripe for sustainable progress. Our transportation infrastructure is one of the largest and most energy intensive systems that our country needs to function. As a result, every time a mode of transportation is pitched it comes laden with facts and figures as to how it is responding to our needs for increased efficiency. But across the board, how do all of these various players (hybrids, buses, planes, trains) stack up in the amount of energy it takes to get someone from one place to another?

With a growing pressure from the government, our economy is beginning to weigh the costs and benefits of reviewing our means of transportation and deciding which deserve promotion while others are best left unaided. Only last week President Obama announced his landmark (albeit under-funded) promotion of High Speed Rail with the doling out of $8 billion in loans. As Americans, our transportation choices decide the course of huge amounts of GDP. When one considers automotive sales, public transit funding and commercial aircraft the order of magnitude is already in hundreds of billions of dollars. It is no surprise that industries are all fighting to shift the course of the next two decades towards their respective products.

With a range of difficult products hitting the market at a range of different scales, the comparisons can often end up being apples to oranges. Boeing’s new 787 Dreamliner is supposed to be 20-30% more fuel efficient than it’s industry counterparts, but does that make it more efficient than HSR or a 2010 Toyota Prius? New York City has a growing fleet of hybrid-electric buses, but these upgraded vehicles actually only get 3.5mpg. How does that compare to taking the subway or driving yourself? I thought it was helpful to get everything on the same field and see how the options stacked up.

In this case the metric of choice is British Thermal Units (BTU) per passenger mile. One BTU is the amount of energy needed to heat one gallon of water one degree Fahrenheit. One gallon of regular gasoline has around 115,000 BTUs of latent energy. When calculating for passengers I assumed a 75% capacity across the board except for SUV’s and Hybrids where I assumed 2 passengers (Given we are in America, I think it can be agreed that is generous.) If one was driving solo then double the numbers below.

Disclaimer: Before the pointing out of caveats ensues, this is not a doctoral thesis. It is a comparison made through research and math that took hours instead of months in order to give some perspective to common transportation options. There are countless factors that contribute to the final energy usage of many of these modes of conveyance, some of which I note below, but the basics are here.

I found the results revealing. Using the average estimate of HSR energy consumption of 0.086 kwh per passenger mile, the speedy trains make a remarkable comparison to our standard transit choices. Though the BTUs used per passenger seem close to a 2010 Prius, a single driver would deteriorate some of the car’s relative attractiveness (though still keeping it well ahead of others.) New York’s hybrid-electric buses are a stand-out. Even when only 75% full they beat the train and the subway by a healthy margin and certainly make more sense than people driving cars (even green ones) alone into the city. Despite Boeing’s efforts for efficiency, plane fight is still much less efficient than going by train. Rather it is merely a convenience that our society has grown accustomed to, though one that HSR could eventually put on the chopping block.

Cruise ships also stood out, but as the black sheep of the bunch. I have read more than once how the shipping industry is primed for lowering our energy usage, but vacations taken on cruise ships are deplorably wasteful with fuel usage as low as 50 ft per gallon in stiff winds and rough seas.

The first hidden factor not included in these numbers is the latent energy within fossil fuels. Some estimates allocate 2.73 kwh of energy (9,317 BTUs) to refining a single gallon of gasoline, adding another 8% to its usage. This would change for different vintages: high octane, ethanol, jet fuel. Even that does not include drilling for oil, shipping the crude, crating the gas and shipping that to its respective consumer.

Perhaps the biggest “but!” about the breakdown is that the systems run off of electricity have their relative efficiency in BTUs operate as a direct factor of where they are getting their power from. A Combined-Cycle Gas Turbine (CCGT) that burns natural gas for electricity could easily be built today to reach 60% efficiency, even more if co-generation is utilized with the waste heat. Yet that would mean that it would take 1.7 kwh of natural gas energy (5,802 BTUs) to create 1 kwh (3,413 BTUs) of electricity. Theoretically, if the NYC Subways were running entirely off of wind power then their impact would be minimal whereas coal powered HSR trains lose some of their luster. This is often the basis for the argument against plug-in-hybrid electric (PHEV) or electric vehicles(EVs) given that the net reduction in greenhouse gases or energy usage is less until our grid efficiency is improved.

While that is true, I think solving the last link of the supply chain is equally as valuable given that all will require time, funding and patience for society to become accustomed to having a new taste in their mouth. If anything, the data reminds us that a combination of solutions will always be necessary meaning that as an interconnected ecology of options there are numerous variables that have to be assessed and improved in order to further the sustainable goals of the system. Though chique, advanced and perhaps even becoming trendy, targeting only HSR is not the answer to our transportation problems. It must be implemented alongside new, smaller, complimentary systems in addition to maintaining the ones we already have.

Notes: For those interested, these are some of the sources for the various numbers I used in calculations:

Photo Credit: Hybrid Car News

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