The state tax haul for Honolulu rail continues to seesaw.

Recently, general excise tax surcharge collections for the project have fallen well short of official projections in one quarter only to rebound and beat them in the next.

Rail officials reported Friday that the project received $60.9 million in general excise tax surcharge collections for the first quarter of 2016, exceeding forecasts in rail’s outdated 2012 financial plan by $2.2 million.

The previous quarter, Honolulu Authority for Rapid Transportation reported that the transit project received $51.2 million to help fund construction, which was $8.4 million less than rail officials had forecast for October through December 2015.

The rail project received $8.3 million more than forecast for the quarter ending September 2015.

It received $8.3 million less than forecast in the quarter before that.

HART officials said Friday that they still don’t know the reason for all the recent quarterly swings.

Overall, the project’s GET collections are tracking about $36 million less than projected to this point, representing a 1.1 percent shortfall, according to HART.

In 2014 rail officials predicted that they would fall short by about $100 million in surcharge funding by the time the tax expired in 2022. It was part of the budget shortfall they presented to the public, and it helped spur state and local leaders to approve a five-year extension of the surcharge.

Rail’s GET surcharge for Oahu is now set to expire in 2027, and project officials estimate it will generate an additional $1.5 billion.

Rail has taken in some $1.69 billion from the surcharge since collections started in 2007, according to HART officials.

As costs climb, it is uncertain whether the extension will generate enough funding to complete the largest public works project in state history.