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Traveling, whether by car or plane, has become a daily frustration and inconvenience for Americans. Because of potholes and closed bridges, congested highways and airport delays, "getting there" often seems impossible.

Last week, in response to public demand that politicians do something to repair the transportation system and increase its capacity, the House approved a $31 billion transportation bill for 1991, which exceeded the White House request by $4 billion.But Congress is missing the central point: As long as some travelers and commuters pay less to use the transportation system than the costs they impose on society by using it, congestion and disrepair will continue - regardless of how much we increase spending.

Suppose, however, that everyone could reach destinations more quickly with less inconvenience and at no extra cost. This sounds like the proverbial free lunch, but economic research suggests it could happen. Bringing it about would require moderate changes in the design of highways and airports, but a major shift in the way we pay for using them.

When a truck uses a road it damages the pavement. The damage depends on the truck's weight per axle. A "pavement damage charge" based on axle weight would accurately reflect the damage and give truckers an incentive to reduce axle weights by shifting to trucks with more axles, thus reducing road-maintenance costs and extending pavement life.

Currently, truckers pay a fuel tax that provides them with the opposite incentive: The tax rises with a vehicle's axles, since trucks with more axles require larger engines and get lower fuel economy.

The major social cost of a car using a road or of a plane using an airport is the congestion it causes. Existing fuel taxes and weight-based landing fees do not discourage use of roads and airports during congested hours.

Regardless of what other policies are implemented - from highway lanes designated for cars with several passengers to limiting aircraft operations - congestion remains. The only solution is to set an explicit price for use that varies throughout the day with the amount of traffic, whether it be on a road or at an airport.

If such pricing changes were accompanied by changes in system design, prices would actually go down. If roads were made thicker, trucks would cause less damage; axle-weight charges would be lower than those truckers now pay to use the roads. If more runways were built, planes would cause less congestion and congestion charges would be lower. In most instances, congestion pricing would lower the cost of air travel.

The upshot would be that society would gain at least $25 billion annually in lower maintenance costs and less delay, at an annual cost of only $3 billion to pay for thicker roads and more runways. An improved transportation system would also bring in calculable benefits to the nation's economy in the form of higher productivity.