Graphic: HNTB

The puzzle of how to pay for new federal investments in transportation is the single greatest stumbling block facing members of Congress — should a gas tax increase be combined with a vehicle miles traveled (VMT) tax? How about a national infrastructure bank that leverages private capital?

A poll released today by the engineering firm HNTB suggests that higher gas taxes could continue to face political headwinds from both sides of the aisle, even after the recession begins to ease.

A 10-cent gas tax increase that would be imposed only after two straight quarters of economic growth faced opposition from 64 percent of respondents, and just 16 percent said gas taxes should be raised to pay for "roads and bridges."

But the poll found strikingly strong support for tolling, particularly congestion tolling through HOT (high-occupancy toll) lanes. One-third of respondents said HOT lanes should be used for future transportation revenue, with 35 percent supporting the use of public tolling and 20 percent backing private tolls.

As with any poll, wording is everything; the above graphic depicts another poll question that referenced high-speed rail in addition to road investments. When the phrasing was changed, support for gas taxes climbed by 8 percent.

And when respondents were asked about "adding" HOT lanes with higher tolls "during rush hour," 68 percent were willing to support the move. As my colleague Ryan Avent has pointed out, however, new HOT lanes can be added without building more highway capacity by simply converting existing lanes.

If lawmakers are looking for data to jumpstart a discussion of broader toll use — particularly on the interstates, which would deliver a blow to the road lobby — today’s poll might be a good place to start.

(The source of polls can often be as noteworthy as their phrasing. Given that, one quick note on HNTB: The firm is currently embroiled in a debate over streetcars versus light rail in Kansas City, according to local media reports.)