A new border crossing between the United States and Canada would handle truck traffic in one of the northern border's busiest trade corridors. The bridge would be about 1-1/2 miles north of the existing Peace Bridge, the third busiest commercial crossing and second busiest overall crossing along the U.S-Canadian border. The Ambassador Niagara Signature Bridge group envisions a $300-million four-lane span for the roughly 6,000 trucks that now cross the Peace Bridge daily and relegating the existing Peace Bridge to passenger vehicles only. The owners of the Ambassador Bridge in Detroit filed paperwork with the U.S. State Department in recent weeks seeking permission to build and operate a bridge across the Niagara River at Buffalo. Operators of the Peace Bridge, who are in the midst of expansion plans to ease frequent commercial backups, oppose the plans, which have been in the works for several years. The Ambassador Niagara Signature Bridge Group is a unit of the Detroit International Bridge Co., which along with the Canadian Transit Co., owns and operates the busiest vehicle crossing along the border, the Ambassador Bridge between Detroit and Windsor, Ontario.