Paying $4 a gallon for gasoline will do more than lighten your wallet and raise your blood pressure.

Over time, it will also alter the basic geography of our lives, transform how we live, work and shop, affect our interactions with one another and change the way we do business. It may even change our eating habits.

JAY BOOKMAN MY OPINION • E-mail Bookman Recent columns: Familiar Georgia may melt away  Slowly, green shoots of optimism appear  Inciting fears in hard times dangerous  Georgia Senate endorses radical idea  'Socialist' charge has lost its power to sting  Legislature, we've got your number  Baseball in spring a metaphor for life

In fact, if you recently passed up that ribeye steak at the grocery because of its $10-a-pound pricetag, the price of gas has already changed your diet. Food is now a petroleum-based product, and as oil costs soar, so does the cost of food.

Thanks to misbegotten government fuel subsidies, for example, vast acreages of farmland are being diverted to raising corn for ethanol production, and that's corn that the cows aren't eating. In addition, most of the pesticides and herbicides used to grow our food are petroleum-based, as are many fertilizers. Fertilizers heavy in ammonia, for example, are critical in grain production. They're created from natural gas, and since the price of natural gas has almost quadrupled in the past 10 years, the price of fertilizer, and thus grain, has soared as well.

Until now, cheap energy also has helped to shape our living arrangements. In places such as metro Atlanta, where the urban core no longer serves as the center of gravity, development has sprawled into suburbs and exurbs. People in search of cheaper housing or more space could just keep driving farther and farther from their job sites until they found housing that met their needs.

But $4-a-gallon gasoline puts a tether around their necks, pulling them closer to the core. With gas prices so high, someone who drives 30 miles to work each morning in a 20-mpg vehicle will have to spend $12 a day just on gasoline.

That's a big bite out of a weekly paycheck, and before long, market forces are going to start driving that commuter to find another solution. You can already see it happening.

Here in Atlanta, property values in the downtown core have held steady or even continued to rise, a product of short, cheap commutes. But the situation is very different in exurban Atlanta.

According to MetroStudy, a real-estate research firm, developers in the northern half of metro Atlanta now have a five-year backlog of lots ready to be built upon. In south metro areas, they have enough lots cleared and served with utilities to meet current demand for seven years. With gas prices so high, it may be decades before those lots in the farthest reaches of metro Atlanta see construction.

Gasoline prices are sending commuters an economic signal, telling them to shorten their drives, and with a little math, the size of that signal comes into sharp focus. Every day, drivers in metro Atlanta travel about 130 million miles. Assuming average fuel consumption of 20 miles per gallon, that's means we use 6.5 million gallons of gasoline a day.

In January 2007, when gasoline was $2.15 a gallon, we spent $14 million a day on gasoline. But if the price rises to $4 a gallon, we'll be spending $26 million daily, an increase of $12 million.

People respond to numbers like that. For decades, it was argued that you could never get Americans out of their big cars, yet last month, sales of light trucks and SUVs fell 17.4 percent compared with April 2007, while sales of cars rose 5.2 percent.

And out in San Francisco, where $4 gasoline is already a reality, revenue from toll roads and bridges is falling while ridership on mass transit is increasing. Similar trends are occurring here in metro Atlanta. According to the Georgia Regional Transportation Authority, the number of vehicle miles traveled per licensed driver in the metro area fell from 58.8 miles a day in 1998 to 44.9 miles in 2005. And express buses from northern suburban counties that once disdained mass transit are now standing room only and are turning riders away.

Four-dollar gasoline can only accelerate those trends. We have built an economy and a society on a foundation of cheap energy, and that foundation is washing away. As a result, changes that once seemed implausible may now be inevitable.

• Jay Bookman is deputy editorial page editor. His column runs Monday and Thursday.