Toll increases aren’t included in the stateThruway Authority’s $2 billion budget for 2015 — but that doesn’t mean they won’t eventually happen.

The big factor may be the new Tappan Zee Bridge.

The authority’s financial estimates show it could see a $305 million shortfall in 2018 — the year the new bridge would open.

E.J. McMahon, president of the fiscally conservative Empire Center, said it’s not certain that tolls will have to go up, but he added that “something has got to give” considering rising expenses and the bridge’s $3.9 billion cost.

The estimated toll revenue for 2014 is $658.1 million, according to Thruway Authority figures. A 2015 budget report prepared for the authority gives a target toll revenue figure of $990.1 million for 2018. According to a footnote, that target “includes additional toll revenues necessary to maintain fiscal balance.”

The extent to which the new Tappan Zee Bridge, spanning the Hudson River between Rockland and Westchester counties, will affect tolls both on the bridge and along the rest of the 570-mile superhighway, has been an open and highly publicized question.

Thruway officials say upstate increases won’t go to pay for the bridge.

But earlier this year, financial writer Nicole Gelinas noted that the bridge tolls ($5 cash) have historically subsidized the rest of the Thruway.

When that ends and the new bridge has to be paid for, officials will have to look elsewhere or to higher tolls to make up the difference. A 2012 proposal to increase tolls 45 percent for truckers was dropped in the face of strong opposition.

Another option, which has also drawn much attention, is the possibility that some of the state’s $5.1 billion windfall could help pay for the bridge. State coffers are swollen this year due to a series of settlements by banks that ran afoul of regulations. That was money which wasn’t earlier anticipated.

Also in the Thruway’s financial plan is the new Transportation Resource Center announced earlier this year by the Cuomo administration.

Under this plan, offices for the state’s Department of Transportation, as well as the state Canal Corp. (which is part of the Thruway system) will be consolidated at the Thruway’s current headquarters on Southern Boulevard in Albany.