America's 10 costliest commutes

By Forbes.com

Gas prices in Texas are among the cheapest nationwide, but that doesn't mean commuting by car is light on Texans' wallets.

Indeed, though the cost of gasoline does matter, other factors, including distance, congestion, car-pooling rates and use of public transit, also play important roles.

Those living in Houston and its suburbs know this. By these measures, the metro area ranks as the nation's ninth most affected by rising gas prices, even though the average driver pays a relatively cheap $3.49 a gallon (as of May 1). Why? About 95% of residents drive a car to work. What's more, sprawl and congestion collude to increase driving times, and clogged highways greatly cut fuel efficiency.

But that's not nearly as bad as Nos. 1 through 5 -- California's "Inland Empire" of Riverside and San Bernardino, Atlanta, Washington, Miami and Chicago, respectively -- where gas prices, traffic and commuting patterns really pack a wallop. Others feeling the pinch: Birmingham, Ala., No. 6; Los Angeles, No. 7; Raleigh, N.C., No. 8; and Sacramento, Calif., No. 10.

Behind the numbers

To arrive at this list, Forbes.com took the country's 50 largest metro areas and looked at congestion, fuel costs, use of mass transit and car pools, and commuting distances to determine which were the most affected by rising gasoline prices and to calculate how much commuters pay each day to get to and from work. All fuel costs reflect May 1 prices.

Using the Environmental Protection Agency's fuel-efficiency curve, we first adjusted gas prices for traffic by calculating what portion of the average commute is driven at maximum fuel efficiency.

"When we're going between 50 and 60 miles an hour, we're burning 23 miles per gallon, but as you drop down to, say, 20 miles per hour, that number is more like 16 miles per gallon," says David Schrank, a research engineer at the Texas Transportation Institute. "As you get more and more stop-and-go, with the emphasis on the stop, you start . . . going nowhere and burning gas."

We calculated commuters' gasoline costs by adding the institute's congestion figures to U.S. census data on the length of the average commute and the cost of metro-area gas prices, based on data from GasBuddy.com, a Web site that tracks gas prices nationwide. We assumed that when roads are clear, cars could get 23 miles per gallon and travel at an average speed of 50 mph. Those same cars, we assumed, averaged 20 mph during high-traffic periods.

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Next, we adjusted the figure on a per-worker basis, taking into account how many drive. That means in cities with a high proportion of car poolers, walkers or public-transit riders, the average commuter isn't as affected by rising gasoline prices.

Take San Francisco, which has some of the highest gas prices in the country, just a hair shy of $4 per gallon. That's certainly more than Birmingham, where gas costs $3.59 per gallon, but because 72% of Bay Area commuters drive to work alone, versus 88% of Birmingham workers, the per-worker gasoline cost of the daily commute was lower in San Francisco: $5.32 per person per day, compared with $6.16 in Birmingham.

Distance also is a factor. In a sprawling metro area such as the Inland Empire or Washington, it isn't simply that gas is expensive and traffic is slow but that residents have to drive long distances. Commuters in these two metro areas travel the farthest, by our calculations, and more road miles mean more gasoline.

Record-high rates

Gas prices vary based on crude-oil prices, which in turn depend on oil output from the world's rigs and wells. Oil has been trading at record highs.

Refining capacity and regulatory costs are factors as well. On the 50-mile drive from Houston to Galveston, Texas, most of the "scenery" consists of oil refineries. And every mile that trucks have to transport gasoline from a refinery to a city increases costs. Gasoline doesn't have to travel far to get to Houston, which helps explain the area's relatively low gas prices.

Regulation tacks on more expenses. It's costlier to do business in New York than in Virginia (which ranks at the top of Forbes' best states for business). The more it costs an oil company to operate in a state such as New York, where labor costs or taxes are high, the more those high operating costs are passed on to consumers.

Clean-air standards also make a difference. California Gov. Arnold Schwarzenegger helped enact some of the nation's toughest emissions standards -- and gasoline that burns cleaner costs more.

Continued: Drive slower and save

READ MORE: GAS PRICES - CHEAP GAS - CONGESTION - GAS REBATE

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