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ST. CHARLES COUNTY, MO (KTVI) – Less than two years old and safety warnings are being posted on a St. Charles County expressway.

A message board tells drivers to use "extreme caution" on the final piece of the Page Avenue extension.

It’s a heavily traveled stretch of highway: Eastbound 364 at the Highway K overpass. It just opened in the fall of 2014 and already there are a couple of big bumps that can knock you for a loop if you're not ready for them.

“Yeah, you just kind of dip right into it, you know, and it kind of just sways you back a little bit,” said driver Charles Nichols.

You feel the jolt both getting onto and off of the overpass. It may not be ideal but it is expected on the nine-mile $115 million stretch of highway. It has to do with the man-made hills that essentially “lift” the highway up to the level of the bridge over Highway K.

“You actually have to build the earth up to get over the other road and that’s called fill. That material consolidates,” said Bill Schnell, MoDOT Assistant District Engineer.

The slabs of roadway running up to the overpass are designed to “give” and settle, he said. Bridges are not. Their foundations are driven into bedrock.

“The bridge doesn’t move and settle because it’s on piling,” Schnell said. “The pavement does settle because it’s on compressible soil. So you have something called an approach slab. The first several of years of a bridge construction you’ll see more movement on a bridge approach slab. It’s actually normal settling.”

The resulting dips are more common in places with St. Louis-like weather extremes, he said. Be warned and take them slow.

“I’d say going over 60, 70 miles per hour, you might take a wild turn,” Nichols said.

Those approach slabs come with pre-drilled holes so that fill material can be injected under them in case of settling.

Workers will inject foam under the bridge approaches to lift them up to bridge level in mid-July.

“It’s considered routine maintenance and costs only a few thousand dollars,” Schnell said.