Tolls are the coming thing. Politicians like the idea of them, as does the transportation fraternity. The public does not. It will be persuaded to accept tolls only when they provide an immediate benefit — which they can, if done right.

The case for tolls was made at a recent Discovery Institute conference in Seattle. It boils down to two things. Tolls can pay for more bridges and roads, and tolls can help get the most out of the bridges and roads we have.

The two ideas tend to appeal to two different groups. At the conference, Jessyn Schor, director of the pro-transit Transportation Choices Coalition, supported tolls for their ability to manage the flow of traffic and encourage people to use transit. Bellevue developer Kemper Freeman objected to tolls because he considered them "social engineering," but said they were all right to pay for specific improvements.

There is a difference in philosophy here, though with a bit of imagination a smart plan might be marketed to both sides.

The state is taking steps in that direction. In late 2008, the 9-mile carpool lane on Highway 167 south of Renton will be opened to participating single-occupancy drivers — for a fee. By "selling excess capacity," said David Forte of the Department of Transportation, the state expects to move 13 percent more people on that lane than it does now.

At Discovery's forum, Kirby Wilbur — the radio host who led last year's campaign to repeal the 9.5-cent gas tax — said he supported that. A member of the audience challenged him: Wilbur had said he would accept a toll for new things only. The lane on 167 is not a new thing. It is there now. Wilbur's answer was that for people driving alone, it would be a new thing to drive in that lane.

So it would.

In the not-too-distant future, we might envision rush-hour tolls on Interstate 5, with the money going to maintenance and improvement of the region's major north-south freeway. The tolls could be set at a level so that traffic speed could be increased to 50 mph, the speed a freeway will move the most cars per hour.

If that were done, one could imagine one commentator saying that the chance to drive on a free-flowing I-5 at 4:30 in the afternoon was a new thing, and worth paying for, and another commentator saying that it was really quite wonderful that more people were riding the bus.