ST. IGNACE, Mich. (AP) - The Mackinac Bridge connecting Michigan's Upper and Lower peninsulas has closed to all traffic for the second time in three days due to falling ice from its cables and towers. The Mackinac Bridge Authority advised motorists Friday to reduce their speed to 20 mph as they approach the bridge and be prepared to stop. It says bridge personnel are stationed at both ends of the 5-mile (8-kilometer) span to provide instructions. The authority says it's monitoring conditions at various points along the structure and when conditions improve, the bridge will be reopened to traffic. Updated information on conditions at the bridge is posted on the Mackinac Bridge Authority website . Also, text alerts are available. The bridge across the Straits of Mackinac also was closed parts of Tuesday and Wednesday.