COLUMBIA, S.C. - Cracks that started appearing on two new Lowcountry bridges while they were being built and continued since they were opened to traffic have the state's top transportation official worried.

The cracking doesn't appear to threaten the structural soundness of the state Highway 170 bridges over the Broad and Chechessee rivers in Beaufort County, said Elizabeth Mabry, executive director of the state Department of Transportation.

But if it continues, the bridges will need more long-term maintenance than usual, she said.

Transportation workers say it will be February - when the bridges have been exposed to a year's worth of traffic and weather - before they know exactly how serious the problem is.

"I know that some cracking is normal," Mabry said. "But the question to me too is how much cracking is normal, and is this normal?"

The bridges are part of the $105 million widening of state Highway 170, which links northern and southern Beaufort County.

They were built by Balfour Beatty, a firm based in England, after the company's bid was $23 million lower than the nearest competitor.

Cracks began appearing on the bridges' decks almost immediately after the concrete decking hardened last fall, and work crews have been busy patching them.

The cracks aren't big - most of them are measured in thousandths of inches. But some of them go all the way through the bridge, allowing moisture to get inside.

If the problem isn't fixed, the steel rods inside the bridge could corrode. But no problems have been seen so far, transportation officials said.

The cracking on the Beaufort County bridges appears to be far greater than on other recently built bridges in the Lowcountry, said Aubrey Swofford, a retired engineer.

A recently reviewed bridge in Charleston County had about 572 feet of cracks per mile, the most of any of the other bridges Swofford examined. The Broad River bridge has more than 14,000 feet of cracks per mile, according to Swofford's calculations.

Workers are trying to figure out what is causing the cracking. One theory is the Beaufort County bridges are designed differently from others around the state. Some officials think the cracks will stop in a few months.

Any repair costs over the next decade will have to be handled by the builder if the state accepts the work and the current contract is finalized.

The state temporarily has withheld about $5 million of the contract from Balfour Beatty, said Tony Chapman, a deputy state highway engineer.

About $3 million is in fines because Balfour Beatty finished the project late. The other $2 million is being withheld to ensure the state can finish the project if the company can't, Chapman said.

"We're not going to let the contractor get off with a project that's inadequate," he added. "We think the company will finish the work. It's really a matter of when."

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Information from: The Island Packet, http://www.islandpacket.com/