The Ambassador Bridge, a busy international border crossing linking Windsor, Ontario, with Detroit, was closed for five hours on Monday following a bomb threat.
But investigators using bomb-sniffing dogs found nothing suspicious and the span reopened to traffic early Tuesday morning, authorities on both sides of the border said.
"No bomb or device was detected on the bridge," Detroit's emergency management agency said in a statement. It called the incident "closed."
Police on the Canadian side began removing barriers and allowing vehicles back onto the 7,500-foot (2,286-meter) bridge shortly after 1 a.m. EDT (0500 GMT), a dispatcher with the Windsor Police Department said.
The shutdown of the busy crossing came less than a week after the Detroit Windsor Tunnel, a nearby cross-border route, was closed by a bomb hoax.
In a statement, the Detroit International Bridge Company said Detroit police received the threat shortly before 8 p.m. EDT (0000 GMT).
The company said the threat was "similar" to the one that closed the tunnel last week -- but provided no additional details.
While authorities investigated the threat, traffic was diverted to the Detroit Windsor Tunnel as well as the Blue Water Bridge, said Scott Vetor, a supervisor with the Windsor Police.
The Ambassador Bridge, which opened in 1929, is the busiest commercial border crossing in North America and is a particularly important route for commercial traffic.
More than 25,000 vehicles, many of them trucks, use it every day to pass over the Detroit River.
The bridge is owned by Detroit billionaire Manuel "Matty" Moroun.
(Editing by Philip Barbara and Lisa Shumaker)