We've been hearing for a while that the steady drop in US fuel prices are hurting sales of fuel-efficient cars like hybrids and plug-ins. As far as driving habits, though? Lower prices are the pump are having little impact on how much people are behind the wheel, according to the US Energy Information Administration (EIA).

In short, gas prices are down more than a dollar from their 2014 peak of about $3.70 a gallon in June. But gas prices would have to fall as much as 50 percent in order to boost automobile travel by as much as one percent, according to the EIA.

That wasn't always the case. Two decades ago, a 12-percent drop in gas prices would push up automobile travel by a percentage point. The difference, the EIA says, is that people could be more set in their ways now when it comes to driving habits. Additionally, vehicle-miles-per-capita driven has fallen as urban sprawl has slowed and many city dwellers have opted for public transportation or biking.

This could all be a good thing. If gas prices fall further, it doesn't necessarily follow that people will be ditching their bikes or train route for their cars. On the flipside, though, more people may opt for gas-guzzlers and fewer may choose high-MPG vehicles. And we're not the first to think up this theory. National Public Radio in October surmised that dropping gas prices were crimping sales of the Toyota Prius and other hybrid models sold in the US. Check out the EIA's press release below.
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Gasoline prices tend to have little effect on demand for car travel

Source: U.S. Energy Information Administration, based on Federal Reserve Bank of St. Louis
Note: VMT is vehicle miles traveled. Per capita figures reflect U.S. population age 16 and over. Vehicle miles traveled figures are 12-month rolling averages.

The U.S. average retail price per gallon of regular motor gasoline has fallen 28% from its 2014 peak of $3.70 per gallon on June 23, to $2.68 per gallon on December 8. However, this price decline may not have much effect on automobile travel, and in turn, gasoline consumption. Gasoline is a relatively inelastic product, meaning changes in prices have little influence on demand.

Price elasticity measures the responsiveness of demand to changes in price. Almost all price elasticities are negative: an increase in price leads to lower demand, and vice versa. Air travel, especially for vacation, tends to be highly elastic: a 10% increase in the price of air travel leads to an even greater (more than 10%) decrease in the amount of air travel. Price changes have greater effects if the changes persist over time, as opposed to being temporary shocks.

Automobile travel in the United States is much less elastic, and its price elasticity has fallen in recent decades. The price elasticity of motor gasoline is currently estimated to be in the range of -0.02 to -0.04 in the short term, meaning it takes a 25% to 50% decrease in the price of gasoline to raise automobile travel 1%. In the mid 1990s, the price elasticity for gasoline was higher, around -0.08, meaning it only took a 12% decrease in the price of gasoline to raise automobile travel by 1%.

EIA's Short-Term Energy Outlook (STEO) uses a price elasticity of -0.02 to estimate and forecast consumption of motor gasoline, while also considering anticipated changes in travel demand and fuel economy. The December STEO expects that gasoline prices in 2015 will be 23% lower than the 2014 average, and consumption in December will be virtually unchanged from year-earlier levels, as increased fuel economy balances out increases in vehicle miles traveled in response to lower prices and other factors.

Price elasticities can be difficult to interpret, as demand can change for reasons beyond changes in fuel price, including changes in other economic factors (e.g., income), demographics, driver behavior, vehicle fuel efficiency, and other structural factors. Some possible explanations for the decline in gasoline price elasticity in recent decades include the following:

The slowing of per-capita vehicle miles traveled (VMT). After increasing for decades, VMT per capita slowed in the late 1990s and even declined in recent years.
The retirement of the baby boomer generation, because retirees tend to drive less than the working-age population.
Population migrations to urban area, as opposed to rural and suburban areas, because urban residents typically drive less.
Declines in licensing rates for teenagers, as young people delay or avoid getting their drivers' permits and licenses.
The reduced share of household income devoted to motor gasoline expenses. As gasoline represents a smaller share of household expenditures, drivers may be less sensitive to fluctuations in price.

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