LITTLE ROCK — State highway officials Wednesday cautioned motorists to allow extra time to navigate the Interstate 430-I-630 interchange or avoid the state’s busiest intersection altogether during construction over about the next three weeks.

Beginning Thursday, construction will take place around the clock at the "Big Rock" interchange in west Little Rock and traffic will be diverted seven times over the next 20 days as crews use two 500-ton cranes erect 40 heavy beams necessary for the elevated, or "flyover," ramps between the two interstate highways, state Highway Director Scott Bennett said.

Bennett also urged drivers who do traverse the interchange to pay close attention all traffic signs in the construction zone.

The first lane change will shift the existing I-430 southbound lanes to what the state Highway and Transportation Department called "collector-distributor lanes" that run beside the main lanes on the west side of the highway.

"There are some bigger changes that are coming … that are really going to impact a lot of traffic in the area," Bennett said during a news conference at AHTD headquarters.

While officials estimate this phase of the project will take about 20 days, weather conditions could cause delays.

"As far as striping the new lanes and things like that, rain could alter it," Bennett said. "As far as hanging the beams, it’s not necessarily rain, but it’s things like lightning or wind that could alter their plans."

Updates on the lane shifts and the entire project are available on the highway department’s website.

Highway construction crews are in the middle of a $125 million upgrade of the interchange that began in 2009 and is expected to be completed in 2014.

The project, named "Big Rock" because of a large sandstone rock formation discovered last year while tearing down a hill to build a new lane to Baptist Health hospital, will include "flyover" lanes between the two interstates to replace the existing exit and entrance loops and a ramp from Shackelford Road for traffic between Financial Center Parkway and I-630.

The project also includes expanding I-630 from the interchange east to John Barrow Road and rebuilding the I-430 overpass so it can accommodate a wider I-630 underneath.

Bennett said the original plan was to erect the flyover beams over a longer period of time, but he said that would have taken months and included total shutdown of traffic periodically for 15 minutes at a time.