OLYMPIA, Wash. -- After being closed for three days, DOT crews partially reopened I-5 in Lewis County Thursday evening.

Crews reopened one lane of traffic in each direction at 5 p.m., but only to large commercial trucks over 10,000 gross vehicle weight. WSDOT will open the freeway to passenger vehicles and smaller commercial vehicles after a second lane in each direction is open, but that is not expected to occur until sometime Friday.

A 20-mile section of I-5 was shut down in both directions Monday when the Chehalis River swelled to record levels following days of rain.

With Christmas just weeks away, UPS drivers are back on the streets in southwest Washington as the flood waters from a deadly storm begin to recede.

Trucking companies and the businesses that rely on their deliveries had anxiously awaited the reopening of the state's main artery, Interstate 5.

The flood-related closure halted traffic between Portland, Ore., and Seattle on a portion of the freeway that normally carries about 54,000 vehicles a day.

High water also prevented the use of nearby detours, with some trucks heading as far east as Yakima to get around the blockage.

Dealing with the blockage - and the detour - has been tricky.

"There is a huge cost when you look at how you have to redo your trucking fleet, to go on alternate routes, to make sure we can get product to the stores," Cherie Myers, Northwest regional spokeswoman for Safeway grocery stores, said Thursday.

She said Safeway was not having trouble getting products from its Auburn distribution center to its stores, including those in the hard-hit areas. The problem has been getting products south of the state to the distribution center.

"You have a lot of vendors and suppliers that come from the south to the north and of course they're being held up, or they're going the alternate routes and it takes longer," she said. "Right now we're OK. We wouldn't be able to be OK if this thing went for another week."

State Transportation Secretary Paula Hammond said 10,000 trucks and 44,000 passenger vehicles use I-5 through the region every day, and delay costs for truckers alone have been about $4 million each day that vital link was out of commission. The total cost to businesses and the state economy as a whole is not yet known, though Gov. Chris Gregoire has said that total damage from the storm could reach the billions.

In addition, four Washington deaths have been blamed on the bad weather and related power outages, and one person has been reported missing.

Gregoire said the occasional flooding of I-5 is crippling and that the local, state and federal governments need to break through their impasse and come up with a permanent fix.

At a news conference Thursday, she talked about the huge losses racked up by freight haulers and businesses both large and small.

"We can't afford to have the economy stymied," she said. "We cannot afford it, literally cannot afford it."

In Centralia, UPS driver Dave Morgan was back to work on Wednesday, making deliveries on a street lined with ruined carpets, soaked mattresses and assorted debris being chucked out of homes.

Driving through water that sometimes went up to the second step of his high truck, Morgan said it was important to try to bring some normalcy back to the neighborhoods that have been hardest hit.

"People are surprised to see me," he said.

Morgan said that on Tuesday, UPS in the area didn't send trucks out at all.

UPS spokesman Dan McMackin said that aside from the hardest-hit area in Lewis County, the impact to company deliveries was minimal, though one of the challenges was the loss of the wireless network in the area, affecting the company's ability to call customers and connect with drivers.

To deal with traveler delays, Horizon Air added flights on the Seattle-Portland, Ore., route this week, as well as upgrading five of its flights to larger jets.

Dan Gatchet, president of Seattle-based West Coast Trucking, said the road closure and detours have been costing his company up to $6,000 a day. He said whereas one driver would make a Seattle to Portland delivery and return in one day, with I-5 closed that driver had to spend the night in Oregon, and another driver had to be sent out to make the same run the next day.

"Productivity is cut in half," he said.

DOT crews got their first look at most of the flooded stretch of I-5 on Wednesday after the water began to recede. They say there's more than 100 feet of pavement damage near the West Street overpass in Chehalis. The pavement's base is also damaged.

The DOT has over 100 crew members working to clear debris along the freeway and have enlisted contractors to help with emergency repairs.

At one point Tuesday, officials said a three-mile section of the road was under as much as 10 feet of water.

As passenger cars traffic waits for the freeway to reopen, alternate routes include the SR-7 bypass or the long route through Eastern Washington.

For a full list of detour routes, click here.

Here's a detour map from WSDOT:

This isn't the first time floodwaters have blocked I-5 at Centralia-Chehalis. It also happened in 1990 and 1996.