Eleven lampposts dinged by snowplows on the new Lowry Bridge connecting north and northeast Minneapolis have been taken down and will be replaced, costing taxpayers $18,000 for what Hennepin County’s top engineer acknowledged Tuesday was a design flaw.

Engineers discovered after a December snowstorm that the bridge’s 54 lampposts were too close to the street. The top of a snowplow blade damaged 11 of the posts badly enough that Hennepin County took them down so they wouldn’t fall into the street. The county will replace them in the spring.

“This is one where experience is a good teacher. Who knew? Well, we should have,” said Jim Grube, county engineer and transportation director. “I take responsibility. I signed the plan.”

The new bridge over the Mississippi River opened in October, replacing a rusty century-old span with open grates. The bridge project began in 2007 with a planned $36 million cost. The design plans eventually expanded to a “signature” bridge with a price of $104 million. While some groused over the burgeoning price, the bridge’s supporters touted it as an investment in the riverfront’s revitalization.

The bridge opened amid ­celebration in October, but surprises remained.

In another delay, the bridge’s $1.58 million ice prevention system didn’t operate this winter. Grube said the vendor changed the system that runs the ice blocker and would no longer provide service for the system Hennepin County was to use. The county chose to wait for the new system so the vendor would support it. He said the cost remains the same for the new system.

The bridge’s median contains spouts that will spray a chemical on the bridge that prevents ice and snow from adhering to its surface, Grube said.

Grube said the county agreed to wait for the new ­de-icing equipment but was surprised by what happened to the lampposts. After the bridge was plowed in December, “somebody saw something” amiss with the lampposts and alerted the county, Grube said. He didn’t blame the county’s plow driver, saying that given the weight and sound of the truck and the washboard-like texture of that snowfall, the driver wouldn’t have noticed knocking against a pole.

The problem is the distance of the lampposts from the street. Normally, Grube said, lampposts are placed at least 2 feet back from the face of the curb so car doors don’t knock them when drivers park at the curb and passengers climb out of the vehicles.

Because the Lowry Bridge’s posts went behind the safety railing, Grube said the posts were placed about 8 inches back from the curb. It wasn’t enough. The space didn’t account for the curve of a snowplow’s top blade that reaches out about 8 inches ­further than the edge of the blade on the ground.

“We thought the rail itself would protect anything else behind the rail from being hit,” Grube said. “We didn’t realize it [the blade] sticks out that much.”

Of the 32 poles hit, two sustained enough damage that they were taken down immediately. Nine others were taken down after an inspector determined they were at risk of collapsing, Grube said. An additional 21 posts suffered only cosmetic damage, and 12 weren’t hit. The county salvaged the light fixtures and wiring so only the posts need to be replaced. Orange construction cones mark the spots of the removed lampposts.

Even though the replacements will go in the same spots, Grube said with certainty that future plows won’t hit them. “You learn from your mistakes, and this is something you won’t forget,” he said.

The taxpayers covered $66.5 million of the bridge. The county financed two-thirds of the project with bonding. The rest came from $37.5 million in state bridge bonds, $2.7 million from Minneapolis, a $475,000 federal transportation grant and $190,000 from Xcel Energy for bridge conduit space.