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SAN DIEGO — Work to bring improvements to Interstate 5 in the North County is scheduled to begin Tuesday, according to Caltrans.

Crews will begin removing vegetation and fencing off construction areas in Solana Beach and Cardiff-by-the-Sea. The vegetation that’s removed will be replaced by non-invasive landscape native to the region’s coastal zone, including almost 400 trees.

The work will take about six weeks, and will be done on weekdays between 7 a.m. and 5 p.m., with some intermittent night work, according to the state transportation agency.

During the project, the part of the San Elijo Lagoon trail just east of the freeway will be closed to maintain public safety.

The work is part of the first phase of a 40-year program to upgrade the coastal transportation corridor.

Called “Build NCC” — for North Coast Corridor — the project includes extending the carpool lanes on Interstate 5 in each direction through Encinitas and Carlsbad; double-tracking the rail line from Cardiff-by-the-Sea to Solana Beach; replacing the highway and rail bridges at the San Elijo and Batiquitos lagoons; restoring the San Elijo Lagoon; and constructing nearly 10 miles of new bike and pedestrian trails.

Construction on the first phase is expected to be completed by 2021.