A mistake of less than an inch will mean a bit more freeway construction work for north metro motorists.

An unexpected 5/8-inch dropoff between the shoulder and newly repaved roadway on an 8-mile stretch of Interstate 35 means crews will be redoing the shoulder and rumble strips to make the surface even. Officials expect the fix to be completed in a couple of weeks.

"We made a mistake," said Kevin Gutknecht, a spokesman for the Minnesota Department of Transportation. "It's a safety issue and we'll get on it right away." The contractor was hired to repave the stretch between Hwy. 8 in Forest Lake and Hwy. 95 in North Branch, repair culverts, install guardrails and make other improvements. But the contract did not call for shoulders on both the inside and outside lanes to be upgraded, resulting in the slight dropoff between the new traffic lanes and the shoulders.

"This is a rare oversight," said MnDOT spokesman Kent Barnard. "This is an easy fix. The shoulders will be better."

The original cost for the project was $9.1 million, but the cost would have been higher had the shoulder work been included. It was not immediately clear how much the re-do will cost, but taxpayers will not pay for the work to be done twice, Barnard said.

Drivers have endured a year of delays and lane restrictions since the project began. Amid the re-do work, MnDOT said, southbound lanes will not be closed during morning rush hour and northbound lanes will not be closed during evening rush hour. Work will be done during non-peak hours, Barnard said, which will exclude weekends.

Tim Harlow • 651-925-5039 Twitter: @timstrib