VMT Trend Continues Flat in the Face of High Gasoline Prices; Update

 

This is an update of a chart from two earlier posts.  Although there was a slight uptick in 2013, the VMT (vehicle miles traveled) trend continues to be essentially flat.  From the 1930s until recently, with a few interruptions, VMT in the U.S. grew consistently.  The inflection point in the curve appears to be around 2004, when the price of gasoline rose above $2.00 per gallon. The current period of flat VMT is the longest since WW II, when gasoline was rationed.  VMT are strongly correlated with economic activity.  For more on the economic aspects of the recent VMT trend, and a discussion of the likelihood that constraints on the global supply of petroleum are involved, see a recent presentation at Columbia University by energy analyst Steven Kopits.   

VMT and Gasoline Price Trend Update

This is an update of earlier data presented in my May 17, 2011 post.  Although there are fluctuations, it looks as if the flat, probably slowly decreasing, VMT trend continues.  It's hard to see how this could not be related to the historically high price of gasoline.

Will this flat or declining VMT trend continue?  It likely depends to a large degree on the price of gasoline, which in turn depends on the price of crude oil.  Currently, U.S. oil production is surging because of the horizontal drilling and hydraulic fracturing that is unlocking tight oil from shales such as those in North Dakota and southwestern Texas.  Will U.S. production grow enough to offset flat or declining oil production in the rest of the world?  Time will tell. And perhaps some of us are finding ways to function well without so much driving, so the flat or declining VMT trend will continue regardless of the price of fuel.

A related issue is the Keystone XL pipeline.  Some argue it should be approved because it will lead to lower gasoline prices.  But, gasoline prices are linked to the world price of crude oil.  The XL pipeline would allow the current moderate surfeit of crude oil that exists in the central U.S. to reach the world market.  Unless the growing quantity of crude oil now being produced in the U.S., augmented by (carbon-intensive!) oil from the Canadian tar sands proves to be enough to lower world oil prices, the XL pipeline is unlikely to lower the price of crude or gasoline to U.S. consumers.  It could lead to higher prices because with the pipeline in place the oil land-locked in the central U.S. could be sold for the higher world price.

Could it be that the high price of gasoline will gradually make driving less important in our way of life?  Could we become increasingly efficient in moving goods, information, and ourselves in ways that don't require so many vehicle miles traveled?  Perhaps, at least to a slight degree, this is already starting to happen, and some carbon can stay in the ground.

VMT Trend Flat - the End of an Era?

Vehicle miles traveled (VMT) are strongly linked to the American way of life, and correlated with economic activity. From the 1930s until recently, with a few interruptions, VMT in the U.S. have grown consistently.

But around 2005, well before the recent economic downturn, an inflection point in the long-term trend appears to have occurred. Since then, the VMT trend has essentially been flat. This is a change of potentially historic proportions.

The 2005 growth cessation coincided with the price of gasoline rising above $2.50 per gallon. As the chart below shows, there have been only two other periods since the 30s when the real price of gasoline rose above $2.50 per gallon, the World War II era and the mid-70s through the early 80s. These periods also saw flat or declining VMT.

The current period of flat VMT is the longest since WW II, when gasoline was rationed. With gasoline prices again nearing $4.00 per gallon, it is unlikely that VMT will increase in 2011. It would not be a surprise if prices increase, and if a decline in VMT sets in. We may be witnessing the end of an era.

Still in Service - Why?

My 1985 GMC S15 pickup is still in service. Why? Economics seems reason enough to a penny-pincher like me, but there’s more to it.

The economics are simple. Long since paid for, this truck’s costs are essentially limited to fuel and repairs. There’s no need for more than liability insurance. Repairs don’t amount to much; it’s only driven 3,000 miles per year, and I have a good friend who’s an expert mechanic. Junkyards are full of parts. Payments on a newer truck might be $300 a month or more. If you divide that by the number of times a month I start it up, maybe 15 times, it’s as if the old truck spits out a $20 bill every time I turn the key.

A bigger issue though is the environmental and safety impact of a vehicle. This truck emits about three times the carbon monoxide, nitrogen oxides, and hydrocarbons per mile as a new truck would. But in most parts of the country, the air is cleaner these days. Driven as little as it is, the contributions of this truck to the dwindling air pollution problem seem relatively trivial. The safety issue is more problematic; this truck has no air bags, no anti-lock brakes. Yet, since it’s mostly driven locally and during the daytime in good weather, I estimate my chances of staying alive with it aren’t too much worse than they’d be with a new truck. Neither of these impacts seems to rise to the level of truly important to me.

Evidence is building, however, that there’s an environmental problem that’s far bigger than emission of conventional air pollutants. This is climate change, which is clearly driven by greenhouse gases emitted by human activities. The best reason to keep an old vehicle on the road may well be its fuel-efficiency compared to a newer vehicle, since burning gasoline emits carbon dioxide, the major greenhouse gas.

The energy tally for motor vehicles has two main components; the energy used in producing a new vehicle, and the energy used in driving it.

It takes about 80 gigajoules of energy to produce a light-duty motor vehicle, including mining and producing the metals and other materials, assembly, and end-of-life recycling.[1] This is a vehicle’s “embedded energy.” It translates to approximately 5 metric tons of carbon dioxide emissions. Once on the road, combustion of a gallon of gasoline releases about 8.9 kg carbon dioxide. At 25 miles per gallon, driving 12,000 miles therefore releases over 4 metric tons of carbon dioxide. So, over a ten year lifetime, the carbon dioxide emitted by driving far outweighs that emitted from producing a vehicle. Keeping a vehicle longer improves the ratio of embedded to operating energy still more. For most drivers then, it makes sense from a greenhouse gas perspective to junk an old vehicle in favor of a new one if the new one is significantly more fuel-efficient.

But that’s a problem, because there aren’t more fuel-efficient trucks available in the U.S. market! This truck was designed in the 70s when the nation cared a lot about fuel economy. It is small and simple. It has no power steering, no power brakes, no power windows. It gets 28 mpg on the highway. Amazingly, even if I wanted to, I couldn’t buy a new truck that gets better mileage than this truck. Most new trucks have far worse mpg. So until more fuel-efficient trucks are on the market, or until some truly major repair is needed, I’ll continue to drive the most beat-looking truck in the parking lot. And I’ll continue to enjoy its major side-benefit of, in effect, sliding a $20 bill into my wallet every time I start it up.

[1] Stodolsky, F., A. Vyas, R. Cuenca, and L. Gaines, 1995, Life-Cycle Energy Savings Potential from Aluminum-Intensive Vehicles, Argonne National Laboratory, Argonne, IL 60439

Electric Cars and Coal

Full battery electric vehicles are claimed to reduce greenhouse gas emissions by 50% to 75% compared with conventional gasoline-powered cars. As discussed below, a realistic percentage reduction is probably considerably less. And there’s a major problem with electric cars. Their large-scale adoption could ensure that the current generation of carbon-intensive coal-burning power plants continues to operate far into the future. An excellent case can be made that coal combustion must be phased out to avoid dangerous climate change. (See, for example, the book Storms of My Grandchildren, by James Hansen.) This phase-out is unlikely to happen if the industrial world tries to power its transportation system with electricity.

Electric motors seem ideal for vehicles because they are highly efficient – they turn about 90% of supplied energy into motion. But powering them from batteries offsets some of this efficiency. Batteries aren’t so efficient. Energy is lost when they supply power, and it is lost when they are charged. Assuming an overall charge/discharge efficiency for batteries of about 65% seems reasonable. Production of electric power is less efficient still; the national average is about 35%. The net efficiency of the power system of a fully-electric car is thus about 0.9 x 0.65 x 0.35, or 20%. This is no different than a gasoline engine. Can these efficiencies be improved? Certainly. But it's hard to see how electric car power system overall efficiency could get much better than 30% as long as the power to charge the batteries comes from the relatively inefficient electricity production system.

Electric cars' greenhouse gas emission reduction potential depends to a large degree on the carbon intensity of this system. Overall, U.S. electricity production releases about 1.3 pounds of carbon dioxide per kWh. This is about 25% less carbon dioxide than if the electric power was produced by a fuel with the carbon content of gasoline. In some parts of the country such as New Jersey, which has a lot of almost carbon dioxide-free nuclear power, this rate is lower, and electric cars reduction potential is somewhat larger.

If the U.S. could produce more electricity from renewable and nuclear sources, and from efficient combined heat and power plants, electric cars would look better from a greenhouse gas perspective. But how likely is a major shift in the generation mix any time soon? It seems more likely that increasing numbers of electric vehicles will provide the excuse for electricity producers to keep old coal-burning plants going.

What to do? We could take a fresh look at diesel engines, which are more efficient than gasoline and comparable to even optimistic estimates for full battery electric when the entire power cycle is considered. Diesels can run on low-carbon fuels like natural gas. We could significantly downsize our cars. This would produce major gains in miles per gallon. And we could get serious about making telecommuting work. It's worth looking seriously at the greenhouse gas reduction potential of such changes before we spend huge amounts of money converting our transportation system to full battery electric.