WASHINGTON -- An attempt to stall a major bridge project between Canada and the United States is now in the hands of an American judge after two days of hearings that wrapped up Thursday.

Judge Rosemary Collyer of the Washington, D.C., District Court promised to consider a request for an injunction against the project in a case she acknowledged as complex.

"This is not easy for me," Collyer said as she concluded the hearing, promising to take her time to sort out the various components of a case she described as a mess. She did not speculate on when she might issue a ruling.

The case is the latest twist in the years-long dispute pitting political authorities against the private company that owns the existing Ambassador Bridge, the aging Windsor-Detroit structure that handles nearly one-third of Canada-U.S. trade.

The private company says its effort to build an additional span is being thwarted by bureaucratic red tape from governments in both countries, which favour the public project.

The Detroit International Bridge Co. is working to block the public project from moving forward. It claims to have franchise rights stemming from the 1909 Boundary Waters Treaty. Now it's asking the court system to intervene before the rival bridge gets its last major U.S. permit -- which would set the stage for construction to begin once it gets funding for a U.S. customs plaza.

It's seeking an injunction that would stop the U.S. Coast Guard from issuing a key permit for the New International Trade Crossing, which would be built almost entirely with Canadian public money.

The very notion that Canada was funding the project drew some barbs from the judge Thursday. She appeared to question how a bridge paid for by a foreign country could claim to have eminent-domain rights and expropriate private homes on the Michigan side.

"(The State of) Michigan can exercise eminent domain with Canadian money?" she asked rhetorically.

"It's going to be a Canadian bridge. We think of it as the Detroit-Windsor bridge. It's really the Windsor-Detroit bridge... Michigan doesn't have any blood in this."

A day earlier, Collyer essentially brushed off the Canadian legal representation in the courtroom, suggesting they had no business being involved.

"To be perfectly frank, I was astonished that Canada thought it needed to jump in," the judge said. "Why don't we not worry about Canada right now?"

The court was then shown slides demonstrating a drop in traffic since the 1990s on the Ambassador Bridge, amid the decline in manufacturing over the last decade.

It only makes sense to build a new span if there's no rival bridge eating away at toll revenues, said Matthew Moroun, the son of bridge baron Matty Moroun.

If the public project goes ahead, there's no economic case for a new private Ambassador span, the younger Moroun said in an interview outside the courtroom.

The company resents having to spend at least $22 million per year to maintain the old bridge when it could be completing a twin span right now, in order to be able to shut down the existing one for major repairs, he said.

"We'd like to build our twin span. We've been trying to build it for 10 years. The governments have been blocking us for 10 years," Moroun said.

"We're throwing money into costly repairs that we could be throwing into a brand new bridge."

Moroun acknowledged why governments would want their own bridge in such a vital trade corridor. But the Ambassador has done a perfectly good job for more than 75 years, he argued.

"And we haven't used any taxpayers' money, either."

Roy Norton, Canada's former consul-general to Detroit, estimated that the Morouns would lose about $30 million in toll revenues each year should the new crossing be built.

They have consistently tried to derail the project, but likely won't succeed, Norton predicted.

"It's a rational economic decision -- if not a very public-spirited one -- to invest a chunk of that $30 million in trying to perpetuate the monopoly."