A "full funding grant agreement" with the U.S. Department of Transportation contains $178.6 million for Central Florida's controversial SunRail commuter train project.

But, according to documents reviewed by Sunshine State News, that "full funding" pledge leaves Florida on the hook for hundreds of millions, if not billions, of dollars.

Though the yet-to-be-disclosed May 2 letter from the federal DOT pledges to cover "50 percent of the total project cost," that share is not guaranteed.

If Florida were to default on any terms of the deal, the state would be liable to repay Washington for the entire amount -- whether the rail line is built or not.

All cost overruns would be paid by the state.

"It's 100 percent risk to the [Florida] taxpayer. A unilateral contract like this would never be considered in the private sector," said Beth Dillaha, head of the opposition group, Veto SunRail.

Gov. Rick Scott has until July 2 to decide whether to approve or reject the 61-mile commuter line that would run through parts of four Central Florida counties.

Critics say SunRail is a worse deal than the Tampa-Orlando high-speed rail venture that Scott turned down. And those critics, including Dillaha, say the governor has an "out" if he wants to use it.

"The agreement calls for a 'stable and dependable funding source'" to cover all costs, Dillaha notes. "There isn't one."

While local governments and the Legislature have ponied up funds for the project, those allocations come nowhere near meeting SunRail's short- and long-term expenses.

State Sen. Paula Dockery, R-Lakeland, says SunRail's price tag has already ballooned, pointing to an FDOT document that pegs the 30-year costs at $2.66 billion -- double the advertised figure.

FDOT is the designated "grantee" of the federal funds, making the taxpayers of Florida -- not just those in the affected four-county region -- liable for any financial shortfalls.

As such, the Federal Transit Administration stipulates that the governor's approval is needed.

"The state is ultimately responsible for cost overruns, completion of the project regardless of federal funds, and for any default on the terms of the agreement," said Dillaha, a former Winter Park city commissioner.

"The state is already paying up to $15 million per year for such miscalculations with Tri-Rail" in South Florida, she noted.

Scott has not indicated which way he will go on SunRail, but he previously cited Tri-Rail's ongoing operating losses as one reason for rejecting $2.4 billion in federal stimulus funds for the high-speed venture.

On the other hand, the governor is under political pressure to move forward with SunRail, at whatever cost.

The Republican-led Legislature set the wheels in motion with preliminary funding just a month before Scott took office, and U.S. House Transportation Committee Chairman John Mica, R-Orlando, pledged to push the needed federal grant money through Congress.