President Obama's transportation department slapped down a suggestion by its own secretary Friday that the government tax motorists based on how many miles they drive rather than how much gasoline they burn.

Secretary Ray LaHood floated the idea in an interview with The Associated Press.

Gasoline taxes for nearly half a century have paid for the federal share of highway and bridge construction, but LaHood said they can no longer be counted on to raise enough money to keep the nation's transportation system moving.

"We should look at the vehicular miles program where people are actually clocked on the number of miles that they traveled," the former Illinois Republican lawmaker said.

Asked about the claim, transportation department spokeswoman Lori Irving immediately shot it down.

"The policy of taxing motorists based on how many miles they have traveled is not and will not be Obama administration policy," she said.

The mileage tax idea has already angered drivers in some states where it has been proposed.

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