Thanks to a constant flow of cars newly assembled on each side of the border and trucks packed with the parts used to make them, the bridge is the busiest border crossing in North America, with 6.3 million trips last year, according to the Public Border Operators Association.

But the location of the Ambassador Bridge, which Mr. Moroun bought in 1979, is not where anyone would consider putting a busy border crossing today. On the Canadian side, there is no direct expressway connection, and a lack of space means that the truck inspection for customs and immigration is miles away.

It is an arrangement that suits neither Windsor’s residents nor bridge users.

After years of political debate and a string of unsuccessful and messy legal challenges by Mr. Moroun (in one tussle in 2012, the businessman, then 84, and one of his executives were jailed overnight in Detroit for contempt of court), a solution is now emerging.

A recently opened expressway will link to a new bridge that the Canadian government will build in an industrial area about three miles west of the Ambassador Bridge.

Mr. Moroun, however, is not yet ready to back down.

For 15 years or so, his Canadian Transit Company gradually acquired houses around Indian Road as part of a plan to build a six-lane bridge beside the four-lane Ambassador and to expand the customs and immigration plaza on the Windsor side. In anticipation, an approach to the new bridge stretches for a block behind Indian Road with unused customs booths at one end and a ramp to nowhere at the other.

But any new bridge needs approval from Canada’s transport minister and the Province of Ontario, and Drew Dilkens, Windsor’s mayor, firmly opposes the idea. In a statement, Transport Canada, a federal department, said it was reviewing Mr. Moroun’s application but offered no timetable for its approval.