The Mackinac Bridge is almost 60 years old. It’s held together in part by nearly six million steel bolts and rivets. Millions of cars and trucks cross it every year. That traffic puts stress on the five-mile span connecting Michigan’s peninsulas. Engineers have used sensors to determine how well the bridge is withstanding that stress. This week, the Mackinac Bridge Authority is installing six new sensors designed to provide better data. Executive Secretary and CEO Bob Sweeney tells WDET’s Pat Batcheller these sensors are unique because they’re self-powered. The bridge opened on November 1, 1957. Click on the audio player to hear the conversation.