ST. PAUL, Minn. (AP) - Cheap gas prices could put a dent in Gov. Mark Dayton's forthcoming proposal to tack a new sales tax on fuel purchases.

Dayton acknowledged Friday that his bid for billions more for road-and-bridge work would fall short if today's surprisingly low gas prices stay that way.

He has said he'll push a $5.8 billion revenue plan for the next decade, with a portion coming from a 6.5 percent tax on gas purchases.

Dayton says the revenue estimate is based partly on gas prices averaging $3.25 per gallon - substantially more than the $2 many motorists are paying now.

As gas prices rise, so would the state's tax take, which is legally dedicated to road construction.

Driving habits change based on fuel prices, so crafting firm tax estimates will be difficult regardless.