Minnesotans probably won't hear a lot of discussion about transportation funding in this fall's campaign for governor. And that may not be a good thing.

A rare consensus seemed to emerge at last week's gubernatorial debates. All three major-party candidates for governor said they would look to bonding to keep the state investing in transportation, especially if receipts from the highway-dedicated gas tax go south in years to come.

That much accord on borrowing for roads, bridges and transit was unexpected, especially given the last decade's partisan strife on the subject. GOP Gov. Tim Pawlenty met with heavy DFL resistance when he made four major transportation bonding proposals between 2003 and 2008. He got the first one enacted, worth $400 million, but met roadblocks thereafter because he refused to support higher taxes to service the new debt he sought.

The 2008 Legislature's DFLers and six brave Republicans finally overrode Pawlenty's veto to put an 8.5-cent-per-gallon gas tax increase into law. The way that increase is structured reveals legislators' determination to adequately service new trunk highway bonds (under the state Constitution, they are the only kind that can be used for state roads and bridges). The total is actually a 5-cent tax increase and a floating 3.5-cent surcharge earmarked for debt service. It backs $1.8 billion in bonds, used primarily to finance bridge improvements -- a felt need in the wake of the Interstate 35W bridge collapse.

In that history lies a lesson for the next governor: Don't come to the Legislature proposing to issue bonds for transportation without a plan for servicing the debt. Minnesota voters deserve to hear as much as well.

Last week's transportation funding comments by Mark Dayton, Tom Horner and Tom Emmer produced frequent mentions of more bonding but scant evidence that they have been formulating plans to service the debt those bonds would generate.

Dayton mentioned a federal program designed to assist states that are constitutionally barred from issuing their own highway bonds. It allows future federal highway grants to be tapped for debt service. But Minnesota Department of Transportation officials and transportation experts agree that those so-called GARVEE bonds aren't well-suited to a state like Minnesota, which can issue its own bonds.

The candidates might say that with the 2008 gas tax increase not yet fully phased in, and with plenty of other problems urgently pressing state government, now is not the time for detailed gubernatorial consideration of future transportation finances.

But they should know this: Several months ago, MnDOT set a new trunk highway fund guideline: No more than 20 percent of expected future state revenues should be committed to debt service. Existing obligations are brushing that ceiling now. More bonding will be a ceiling-buster unless the fund itself grows.

Chances for that growth to happen automatically, as it seemed to through most of the 20th century, aren't good. Anyone who has noticed the increasing number of hybrid vehicles on the road knows why. In 2004-05, Minnesota's gas tax receipts fell year over year for the first time since the 1930s. MnDOT officials regard that dip as a harbinger.

It behooves those who hope to succeed Pawlenty to take that warning seriously. Gasoline consumption may soon dwindle, but the need to safely and efficiently move goods, services and people won't.