Construction on road projects intended to alleviate congestion between La Jolla and Oceanside is slated to begin later this year following the allocation of $103.7 million by the California Transportation Commission.

The San Diego Association of Governments, a regional planning agency, said Thursday the money will be used to extend carpool lanes on Interstate 5 and add a second track to a portion of the coastal rail line in North County.

According to SANDAG, the funding will allow the agency and Caltrans to begin work on the North Coast Corridor Program, a $700-million package of projects.

In addition to the extension of some carpool lanes from Lomas Santa Fe Drive to State Route 78, and two double-tracking projects across the San Elijo and Batiquitos Lagoons, the package includes the addition of bike and pedestrian paths in Encinitas and Carlsbad and the restoration of the San Elijo Lagoon.

Allan Kosup, Caltrans’ director for the I-5 corridor, called the commission’s vote a “pivotal milestone” for the planned improvements.

About a quarter of the funding will come from TransNet, the half-cent sales tax for local transportation projects approved by voters in 1988 and extended by voters for 40 years in 2004.

TransNet funds are administered by SANDAG.