The Transportation Corridor Agencies, or TCA, says the expansion is the least harmful option to help relieve traffic congestion and help move goods along Interstate 5.
"There are 24 million Southern Californians who depend on this big vibrant economy. We need mobility for that," said Jerry Amante, Transportation Corridor Agency Chair.
The proposal would expand the 241 toll road 16 miles from Oso Parkway in Rancho Santa Margarita, to I-5 near Basilone Road, south of San Clemente. The route would cut through San Onofre State Beach Park, which is a popular area. It is also home to several endangered species and well-known surf spots like "Trestles."
"You can surf without seeing a lot of development. If the toll road is built, you would essentially be walking underneath toll road to get to the beach," said Ben McCue, Wildcoast Costasalvaje.
"Trestles is not going to be impacted by project. The road comes in over a mile away," said David Skelly, a coastal engineer.
Others fear the proposal would destroy a Native American sacred site.
"It would come within feet of the designated burial ground," said Angela Mooney Darcy, United Coalition to Protect Panhe.
Last February, the California Coastal Commission rejected the toll road project, saying it would violate the Coastal Act. TCA filed an appeal with the U.S. Commerce Secretary who, after Monday's hearing, has until Dec. 22 to make a decision.
The hearing was expected to continue until 8:30 Monday night.
Officials expect more than 150 people will get a chance to voice their opinion.