The Mackinac Bridge was closed to all traffic Tuesday for a short period. The Mackinac Bridge Authority made the announcement Tuesday afternoon saying ice was falling from cables and towers on the bridge, making it unsafe for motorists. Motorists are advised to reduce their speed to 20 miles per hour as they approach the bridge and be prepared to stop. Bridge personnel are stationed at both ends of the structure to provide instructions. The Mackinac Bridge Authority is monitoring the conditions at various points along the structure. When conditions improve, the bridge will be reopened to traffic.