KEY LARGO, Florida Keys – The Florida Department of Transportation (FDOT) has initiated a four-year program to upgrade the Florida Keys Overseas Highway (U.S. 1) between Key Largo and mainland Florida.

Construction is occurring off the existing highway, minimizing inconveniences for motorists, project officials said.

“Both lanes of U.S. 1 will be open through the construction, with the possibility of occasional night-time lane closures from 9 p.m. to 5:30 a.m.,” said project spokeswoman Patti Jones. “Everyone is very experienced on this project and knows there are only two routes in and out of the Keys.”

The 18-mile “Stretch” crosses the fringes of the Everglades and is one of two roadways that lead into and out of the Keys. The “Stretch” will be updated with a new high-span bridge, a concrete center barrier to prevent head-on collisions, new wider roadbed and numerous culverts to protect indigenous wildlife.

Until April 2006, construction is to be focused on the southern 6.2 miles of the “Stretch.”

The county’s tourism agency plans to use its Web site to update visitors with information on the project.

“The Monroe County Tourist Development Council will use this web site, to keep visitors apprised of unexpected developments that might significantly affect travel times to the Keys,” said TDC director Harold Wheeler.

Jones said occasional nighttime, single lane closures would only occur Sunday through Thursday evenings to minimize impacts on weekend travelers. Jones said an updated list of major Keys events will apprise managers of potential high-volume travel days.

The alternate route into the Keys is Card Sound Road, also known as County Road 905.

Jones said she doubts project work will result in the need to direct traffic to Card Sound Road. However, if so, motorists would be informed by new dynamic messaging signs. The FDOT has also installed video cameras to monitor the “Stretch” from a central office. A free “Road Ranger” service is to help motorists who experience mechanical malfunctions.

Jones noted that a portion of Card Sound Road is to be repaved under a separate effort scheduled to begin in August.

Engineers have divided the “Stretch” work into four overlapping projects starting at Mile Marker 106 at the north end of Key Largo and spanning to MM 126 in Florida City, where the Florida Turnpike ends.