Gasoline approaching $4 a gallon might convince people to do something that state laws and police enforcement have generally failed to do — slow down.

It's no secret that avoiding aggressive driving and lowering cruising speed from 70 mph to 65 mph, or even 60, on interstate highways will save fuel. There is increasing evidence that businesses and even everyday drivers are slowing down due to high fuel costs.

In the past month, it's been reported that some airlines are flying their jets a little slower to save fuel. Southwest Airlines says that it began flying a little slower and expects to save $42 million on fuel costs this year, while only adding a few minutes to the average flight.

JetBlue has added about two minutes to its average flight times and said flying slower saved $13.6 million in jet fuel costs last year.

Northwest Airlines added four minutes of flying time to its flights from Minneapolis to Hawaii and expects to save $600,000 a year on flying that route alone.

With such a significant payback for a few extra minutes in the air, it seems reasonable for airlines to continue this cost-saving trend.

National trucking companies, too, are slowing down to save money on fuel. Con-Way Freight, the owner of the nation's largest fleet of tractor-trailers, has reduced the speed limiters in its trucks to 62 mph from 65, and expects the change to save 3.2 million gallons of fuel. And with diesel fuel selling for more than $4 per gallon, that reduction of 3 miles per hour will save the company about $13 million.

In this region, Pitt-Ohio Trucking is reported to be setting the governors on its trucks at 62 mph, down from 65 and 68 mph.

The American Trucking Association wants the federal government to limit the top speed on all trucks to 65 mph. The ATA suggests that slowing down to 65 mph from 75 can reduce a truck's fuel consumption by 25 percent.

Slowing down to save fuel makes sense. But the physics of pushing a car or truck down the road makes a strong case for slow-down-to-save-gasbecause air resistance increases at a faster rate than miles per hour. It's an exponential relationship that causes a disproportionate increase in fuel consumption when increasing just a few miles per hour, especially at the higher speeds.

And the equation works the other way too: Slowing down a bit can save a higher percentage of fuel consumption than the corresponding speed reduction.

And speed is not the only factor in fuel consumption. One trucking company based in Pittsburgh not only adjusted its trucks' governors down to 62, but it also pays its drivers a bonus when they save more fuel by using more efficient routes or by reducing idling time.

The last time the U.S. Department of Transportation looked at fuel efficiency was 1997, so results of a similar study might be different today. But the results of the 1997 test using multiple vehicles serve as a powerful argument for slowing down — slowing down from 70 mph to 60 mph reduced fuel consumption by 17 percent. Dropping speeds from 75 mph to 55 mph slashed fuel consumption by nearly 31 percent.

It's unlikely many people will be willing to slow to 55 mph on the open highway, but 60 or 65 probably would be acceptable to most drivers, especially as gasoline costs approach, or surpass, $4 per gallon.

The early adopters of the slow-down-to-save-gas driving style might not be well accepted on the highway. But when gasoline approaches $5 a gallon, they might find more company in the slow lane.

There seems to be little doubt that the era of cheap gasoline is over. High fuel costs are causing problems for some companies and real hardships for many drivers.

Not to discount that pain, but over the long run, high gasoline costs will be good for the country because they will create sustained demand for more fuel-efficient vehicles and support for alternative fuel sources, as well as leading to a reduced demand for imported oil.

And if driving a bit slower catches on, it might also make the nation's highways safer.