Six piers constructed as part of a $23-million interchange upgrade in Iowa will have to be modified as a result of a contractor’s measurement error that left them too tall for a planned flyover bridge.

The brick veneer-clad cast-in-place piers, ranging in height from 22 ft to 36 ft and designed by Parsons, were built for the Interstate 35/U.S. Route 30 interchange near Ames by Minnowa Construction of Harmony, Minn. Recent field surveys conducted in preparation for adding a 1,690-ft-long continuous steel deck bridge showed the piers deviated from the specified heights by 3 in. to 6 in., according to Iowa Dept. of Transportation engineers.