Contractors looking to build the Gordie Howe International Bridge are asking for extensions as they prepare their bids, calling into question an already vague timeline for the project's completion.

Officials from the Windsor Detroit Bridge Authority say they still plan to start construction in 2018, but they are already backing away from the previous, more specific start date of next summer.

Bridge authority spokesperson Mark Butler insists, though, that work on the $4.8-billion bridge will begin sometime next year, even if the three teams bidding for the contract need more time to plan.

"We're looking at the reasons why they need more time," he said. "If more time is warranted, we will extend it, but the commitment has always been there. We will have the bridge starting construction in 2018."

Mark Butler

Windsor Detroit Bridge Authority spokesperson Mark Butler says work on the new Gordie Howe International Bridge will start in 2018. (Melissa Nakhavoly/CBC)

The bridge authority says construction can begin as soon as a winning bidder is selected because of preparation work already completed on both sides of the Canada-U.S. border. On the Canadian approach to the bridge alone, Butler said an estimated $200 million has been spent already. 

But he wouldn't give any specifics for a bridge construction timeline.  

"I can't be very definitive about the actual start date," he said. "We've committed to having started construction of the bridge in 2018. We remain committed to that date."

Officials estimate building a bridge at the bustling border crossing will take about four years, once construction starts, putting a completion date some time in 2022. But a more definitive timeline will be mapped out once the final contractor is selected, explained Michael Cautillo, president and CEO of the Windsor Detroit Bridge Authority.

The "construction schedule is part of the proposals that will be submitted by our proponents and we will hear from the proponents how they intend to deliver this project on an aggressive and prudent schedule," he said in a statement issued Wednesday.