LANSING, Iowa — Structural engineers changed their minds about the safety of the old and wobbly bridge across the Mississippi at Lansing. For safety reasons they will rip it down in September. Anyone wanting to drive across into Wisconsin — or the other way — will need to go 40 miles upriver to Dresbach or 29 miles downriver to Prairie du Chein. Another option will be a passenger taxi ferry, no cars, from docks at the bridge site. Engineers have been off-and-on about whether the bridge could handle another winter. The bridge is vulnerable to tremors from an adjacent new bridge, which won’t be completed for another two years.