With gasoline around $3 a gallon, there is a lot of talk about how families can cut down on driving. Advice includes switching to public transportation, leaving the SUV at home.

But while that may be a socially desirable, even patriotic, thing to do, commuters in the Washington area, and probably other big cities with mass transit systems, shouldn't expect to see big savings simply from jumping onto Metro.

Family transportation economics are complex, but an important fact to remember if you're trying to save money is that even if the vehicle sits around with the engine off, gasoline represents only part of the cost of a car, truck or SUV. A larger share stems from capital costs, insurance and other expenses that don't go away. That means savings from switching to public transit may be modest or even nonexistent unless you switch so completely that you can get rid of your car or one of your cars entirely. If you can do that, you may well find a good bit more money in your pocket.

Let's look at some numbers, some from the AAA motor club and some I've extrapolated from their figures, which are based on lower gas prices.

The AAA figured last year, when gas was relatively cheap -- about $1.94 a gallon -- that driving a new Dodge minivan 15,000 miles would cost $8,293 for the year, including about $1,335 for gas. AAA figured in maintenance, tires, insurance, license, registration, taxes, depreciation and finance charges. AAA apparently assumed, though it didn't specifically say so, that the van got around 22 miles per gallon.

At $2.90 a gallon, the cost of gasoline over 15,000 miles would climb to $2,002, pushing the overall cost of a year of driving to $8,960.

Cutting that back to 10,000 miles a year by taking Metro would shave $667 off your gas costs, and the AAA figures it would cut your depreciation, through reduced wear and tear, by $925. Of course, a saving of $1,592 is not to be sneezed at, but how much of that could you really keep?

The answer depends somewhat on individual circumstances -- for example, how much would you save by not parking downtown? -- but doing the subway math suggests that many commuters wouldn't save much, at least in the short run.

For example, a rush-hour trip on Metro's Orange Line from Vienna to Metro Center costs $3.55, or $7.10 round-trip. For 220 workdays a year, that's $1,562 -- all but wiping out the savings from not driving.

Similarly, the tab for a rush-hour trip from White Flint to Metro Center is $3.15. (Metro calls that the "regular" fare; the lower, off-hour fares are called "reduced.") Making that round trip 220 times works out to $1,386, another big bite out of your savings from not driving.

Also, remember that while you may be cutting out your downtown parking fee, Metro's lots aren't free. The tab at Vienna is $3.75 a day and at White Flint it's $4 (though you can pay up to $7.75 there, if you're not careful). Plus, if you want a reserved space at certain lots, it's an additional $45 a month.

Metro, incidentally, has all this information on its Web site, at www.wmata.com. Click on Schedules & Fares, then on Metrorail Fares, then on Metrorail Station page. You can pick any pair of stations and look up the fares, parking fees, travel time and distance.

With that last figure, you can figure the cost per mile. Vienna to Metro Center, for example, is 14.02 miles, or 25.3 cents a mile for a $3.55 rush-hour fare. That's a lot more than the 12 to 17 cents AAA figured for the pure operating costs -- gas, tires and maintenance -- for a range of new cars when gas was "cheap." And it's more than the per-mile costs for many cars even after you figure in today's gas prices.

This is not to suggest you shouldn't ride mass transit if you can. There are numerous societal and personal benefits from doing so that can go along with possible economic ones.

But as you can see, most of the savings to be had would come from disposing of a car. Even in the good old days of a year ago, driving a new four-cylinder Chevrolet Cavalier sedan 15,000 miles cost $7,142 a year, according to AAA. Removing an expense that size would clearly more than offset the cost of commuting by mass transit for most people.

Some are able to do it, though it may require such Washington area strategies as "slugging" (getting a free ride from a driver who needs extra passengers to qualify for high-occupancy lanes) or split-second timing and car handoffs worthy of a space mission.

Some are able to move close-in, to pedestrian-friendly places such as the District, Arlington or Alexandria or Bethesda. The city is seeing an influx of couples whose children are grown and who find apartment or condo living rewarding in a number of ways.

But the problem for many, particularly suburban, families is that getting along without a car, or multiple cars, is impossible. Families typically cope with multiple jobs, schools, sports, lessons and the like that require flexible transportation, which public transit is not.

We have built a society that depends heavily on the car, and for thousands of residents of this area and across the country there is little practical alternative. If, as many experts believe, cheap gas is never coming back, families have little choice but to reduce their driving as much as possible, cut transportation costs in other ways -- such as driving older cars to keep capital costs down -- and keep the heat on political leaders and carmakers to sell vehicles that are much more efficient.

The Internal Revenue Service noted last week that Congress recently made it easier for victims of Hurricane Katrina to deduct casualty or theft losses from the storm.

Normally, to deduct a casualty or theft loss, a taxpayer must subtract $100 from the value of the loss and further reduce it by 10 percent of his or her adjusted gross income. Anything that's left is what's deductible. The new law removes those limits for Hurricane Katrina losses, so the entire amount is deductible.

To qualify, a loss must be attributable to Katrina and it must have occurred after Aug. 24 in the federal disaster area. And you have to itemize to claim it. The $100 and 10 percent limits still apply to losses not caused by the hurricane.

Also, the IRS said, although casualty and theft losses must generally be deducted on the return for the year in which the loss occurred, those resulting from a disaster may be deducted on the previous year's return, which can result in a speedier refund. Since Hurricane Katrina losses are disaster losses, taxpayers have the option of deducting them on their 2004 returns. Those who have already filed for 2004 -- most taxpayers -- can file amended returns for that year.

Nearly three in five workers employed by companies with 1,000 or more employees participated in retirement plans at work last year, but only 16 percent of those at firms with fewer than 10 workers were in such plans, according to the Employee Benefit Research Institute in Washington. A study by the institute also found that 57.8 percent of workers ages 55 to 64 participated in retirement plans at work, compared with 19.8 percent of those 21 to 24.

Taking Metro might be more relaxing than driving, but it won't necessarily save you much money.