After years of political wrangling and posturing, the state and Charleston County have a fresh legal deal to build the last leg of Interstate 526 from West Ashley to James Island.

The breakthrough came Thursday, less than a year after the project seemed dead, and supporters are more optimistic than ever.

"Boom! 526 will be built," former state Rep. Chip Limehouse said.

But much work remains and large questions loom:

How much will it cost? Where will the money come from?

What the new road will look like, an interstate highway or parkway?

Can opponents delay it some more or even kill it?

The answers will determine if and when the first car can drive between Citadel Mall and the James Island connector in less than 8 minutes.

Here's a breakdown of what's known and not known:

What are the next steps?

Charleston County is seeking proposals from engineering firms that, once hired, could restart the permitting process.

Opponents also are considering their next steps.

Meanwhile, the drama will move next to the state's Joint Bond Review Committee, Senate President Pro Tem Hugh Leatherman told The Post and Courier on Friday. No meeting date has been set.

"The Joint Bond Review approved the original 526," he said. "The model they came up with is so different, it has to go back to Joint Bond Review for approval on that project. It’s a new project as far as the committee is concerned. The price changed, the source of money changed."

Leatherman, a Florence Republican who also is a member of the State Infrastructure Bank, voted against the project Thursday, but he did not predict what the committee might do. 

"I will say this: they’re very thorough when they evaluate proposals that come to us. We’re talking about taxpayers dollars, and we’re actually talking about mega-dollars. I’m not against 526, but I am against the way it’s proposed to be funded,” he said. "We'll give it a thorough examination."

How much has already been spent on the project?

The contract approved Thursday says the State Transportation Infrastructure Bank has spent about $40 million.

The county also has spent $117 million on other state road projects, satisfying the match requirement from its original 2005 deal with the bank. 

When will we know how much it will cost in total?

The deal makes it clear the state won't contribute a dime more than the $420 million the bank committed in 2005. That sum once was enough to cover the whole price tag; now it may not even cover half.

The most recent estimate of $725 million is a few years old, and it's also based on making the project a four-lane parkway with speed limits of 35 mph and 45 mph, instead of an interstate with a 55 mph limit.

As the permitting work resumes, the project could change — and that would affect its total cost. A better estimate is expected toward the end of the permitting work.

How much of the county’s half-cent money will be spent on it?

On Thursday, county budget director Mack Gile said the half-cent would be a primary source of the county's portion, estimated at more than $300 million, but exactly how much of it might be needed remains up in the air.

The county's cost also could hinge on how many federal dollars it can secure toward the work.

What other half-cent projects might not get funded as a result?

County Council Chairman Elliott Summey said Thursday the extension would not delay other area infrastructure projects funded from the same sales tax funding source, which is expected to raise a total of $2.1 billion over its 25-year life.

But opponents, such as Jason Crowley of the Coastal Conservation League, are skeptical. One project, a planned flyover at U.S. Highway 17 and Main Road, might not be as crucial if Johns Islanders have a new expressway to West Ashley.

"Anyone concerned about inappropriate government spending of limited taxpayer funds should contact their city, county and state representatives to ask what priority project will be eliminated in exchange for this single road extension," Crowley said.

How much work still must be done before the project gets the necessary permits?

The county estimates it has about a year's worth of work remaining in the permitting process, county spokesman Shawn Smetana said.

Is all the necessary right of way in hand?

As designed, the road will stretch more than seven miles across sections of West Ashley, Johns and James islands.

As work began on the project more than a decade ago, some parcels in that path were purchased already, and further permitting and engineering work will determine how many more will be bought.

When will the public have its next chance to speak on the project?

No public hearing has been scheduled. That said, the public has a chance to comment during regular County Council meetings.

Based on the most optimistic scenario, when might construction begin?

The 526 extension ranks among the most controversial public works project in the history of the Charleston area.

Even under the most optimistic case, the county anticipates construction won't begin for three more years, including one to finish permitting work and two to resolve anticipated lawsuits, Smetana said.

"Perhaps a good government watchdog might be poised to challenge the county’s decision to do a bait and switch on county voters who were duped into voting for the sales tax after being told 526 would not be paid for with those funds," Crowley said.

Again, based on the most optimistic scenario, when might the road open?

Construction is expected to take three to four years, so regardless of what happens, don't plan on driving on the extension until 2026 — at the very earliest.

That's a lot of years, which also could (or could not) bring a lot of political change.

"The world has changed since the Inner Belt Free Way was first proposed in the 1960s," Crowley said. "The public should be pushing back on their elected officials for robbing them of $300+ million for a single road that numerous studies have proven won’t reduce congestion, but simply shift it from one place to another."

Reach Robert Behre at 843-937-5771. Follow him on Twitter @RobertFBehre.