The Portland Bureau of Transportation once again faces a big hole in its budget.

PBOT director Tom Miller informed bureau staff this morning that projections show a $4.5 million gap in the city department's $100 million budget for 2013. 

"This is a shortfall just like last year," says PBOT spokeswoman Cheryl Kuck. "We're looking at $4.5 million in cuts this time around."

Last November, PBOT announced a $16 million shortfall, which it blamed on declining state gas-tax receipts. This year's gap also stems from lower-than-expected gas-tax revenues, according to sources familiar with the bureau's budget. 

"Gas tax is only part of the story," says Kuck. She says other factors in the shortfall are increased PERS commitment, higher health-care costs, and debt proceeds for the $70 million PBOT contributed to rebuilding the Sellwood Bridge.

A study released in August by the energy think tank Sightline Institute showed per capita gas purchases in Oregon hit an all-time low in 2011, and showed signs of another 2 percent decline this year.