Cost of owning a car starts to level out

So you bought a new midsize sedan in 1973, drove it 100,000 miles in 10 years , and then junked it at the end of 1982. The cost of the car when new was $3,493 .

How much did it cost you to keep the car on the road?

If your repair record is average for the 100,000 miles, you spent just 20.6 cents a mile, according to a wide-ranging survey by Hertz Corporation. That works out to 46 percent less than the 38.3 cents that Hertz estimates a 1982 midsize car will cost, assuming no inflation, over the next 10 years.

Thus, you're probably well ahead of where you would have been had you bought another car or two during the same period.

The low overall cost of the '73-model car reflects the significant savings on depreciation, interest, and insurance during the early years of the car. Admittedly, however, today's midsize car is probably a much better vehicle, not only in durability, but in vehicle integrity and safety as well. Also, it pollutes the atmosphere a lot less, assuming the emissions-control system is working as it should.

In addition, today's average intermediate-size car is a foot shorter and 600 pounds lighter than the average 1973 car. And it gets far better gasoline mileage to boot.

The bad part, naturally, is that the midsize automobile now sells for an average $9,387 - or nearly $6,000 more than the '73 car.

Meanwhile, in its latest report on new-car operating costs, Hertz says the rise last year was the smallest since 1976.

The average cost for an individual motorist to own and operate a typical new compact-size US-built automobile in 1982 went up a minuscule 1.25 cents a mile to 44.67 cents - or 2.9 percent above the year before. Contributing to the relatively insignificant price rise were falling interest rates and the sharply lower cost of fuel.

Not included in the figures are garaging and toll costs.

Since 1972, the Hertz survey reports, the estimated cost of buying, owning, and running a typical private automobile has risen 174 percent, although the US inflation rate rose only 129 percent in the same period.

In the last four years alone, the cost of driving a car has soared 63 percent.

''American motorists continued to switch to smaller cars with fewer options, and are keeping them far longer, in an effort to curb the soaring expenses,'' the survey says. And people are driving a lot less, too.

''Average annual per-car mileage is down 22 percent in the past 10 years,'' the survey concludes.

The Hertz survey also took a look at auto costs in 1925. If it cost 11.5 cents a mile in the mid-'20s to own and operate a car for three years, figuring 10,000 miles of driving a year, it would work out to 62.9 cents a mile at 1982 inflation levels - or 16 percent higher than the 54-cent estimate for a midsize car over a three-year period today.

Put in perspective, today's cost may not be as far out of line as is first assumed.