If a bridge is two, then a tridge must be three. These are usually called tri-bridges, There are twelve in the world.
This Tridge is the formal name of a three-way wood footbridge above the confluence of the Chippewa and Tittabawassee Rivers near downtown Midland, Michigan. It opened in 1981 and consists of one 31-foot tall central pillar supporting three spokes. Each spoke is 180 feet long by 8 feet wide.
BTW tridge also refers to three player Bridge (cards).