COLUMBIA — With more than a thousand bridges on South Carolina’s interstates and major highways “rapidly approaching” a need for an overhaul, the state Department of Transportation is asking legislators for a $1 billion commitment to keep the state’s economic lifelines flowing.

Many of the bridges are more than 60 years old, built using designs not intended to handle the quantity and hefty loads of today’s tractor-trailers, according to the DOT. The agency has identified 1,125 such bridges on the state’s main traffic arteries in “fair” or “poor” condition that could become a real problem if not repaired in the next several years.

“Now is the time to start looking at those structures and address them before we have a major issue,” DOT Secretary Christy Hall recently told a Senate panel.

“In other words: don’t let the bridge fall down before you try to address it, or don’t have an emergency closure and then figure out you need to work on it,” she said. “Let’s work on it early.”

She is asking legislators for $200 million annually for five years to do the repairs that will prevent rebuilds that are much more costly, both in dollars and time.

The Senate Finance Committee will consider the request the week of April 3 as it crafts its spending proposal for the fiscal year starting July 1. The version passed by the House in March includes the $200 million allotment specifically for bridge work onmajor highways.

“We have to look at (interstates) as a major lifeline for economic development and prosperity in this state,” Hall said. “What we’ve been successful at avoiding so far is having an interstate bridge closed for a long period of time or detoured for long period of time due to structural issues or a major problem.”

There are notable exceptions to that, depending on what one considers a long time.

In 2015 and again in 2018, portions of Interstate 95 in the Pee Dee were closed due to hurricane-related flooding.The closure of a 13-mile section in 2015 took traffic on an almost 170-mile detour for more than a week as crews repaired bridges that crossed streams and swamps.

Also in 2018, DOT closed the James B. Edwards Bridge on Interstate 526 over the Wando River at Mount Pleasant after inspectors discovered that a 1,000-foot cable in the concrete had snapped due to corrosion. The bridge reopened more than a week earlier than predicted, but that good news came after several weeks of traffic headaches for the Charleston area.

Columbia has been dealing with traffic detours since March 24, when DOT shut down the first five miles of Interstate 77 northbound for nine days. The southbound lanes of the same section will be closed for nine days in April. In all, 17 pothole-ridden bridges will be resurfaced. The complete shutdown of the sections allows the repairs to take days instead of months, according to DOT.

None of those closures are related to the 1950s and ‘60s construction and aging issues Hall is looking to get ahead of. (The I-526 bridge opened in 1991.That section of I-77 opened in the mid- to late-1980s.)

The I-77 repairs were a known issue already in the construction pipeline, said DOT chief of staff Justin Powell.

But the interstate shutdown is an example of what the $1billion request seeks to avoid.

Biennial inspections for every bridge in South Carolina should ensure bridges are closed long before they deteriorate to the point of being in danger of collapsing and risking lives, he said.

As of February, 632 bridges in South Carolina had load restrictions in place, and 51 were closed. Combined, that’s less than 10 percent of all bridges on the state highway system, according to DOT.But the possibility of needing to close any interstate bridge is something the agency is looking to avoid.

Which bridges would be repaired with each $200 million allotment, and in what order, won’t be approved until after the Legislature has committed the money, Powell said.But the priority will be on key commerce routes.

“There are routes in the state where we never want to get in the situation where we get a (load-restricting) posting or closure,” he said, adding, “If we had a closure on I-26, it would be a really bad day.”

Examples of “strong candidates” for being at the top of the list include the I-95 bridge over Lake Marion between Williamsburg and Clarendon counties. The agency pursued a federal grant for replacing that bridge but didn’t get it, Powell said.

“If that one goes down, it’s a 70-mile detour,” he said.

Another is the I-95 bridge over the Great Pee Dee River, which is threatened during floods. DOT did get a federal planning grant for that one, he said.

Follow Seanna Adcox on Twitter at @seannaadcox_pc.