State transportation officials are moving forward with a controversial plan to add toll lanes to a busy stretch of the 405 Freeway in Orange County.

The plan would create two high-occupancy toll lanes in each direction along a 14-mile stretch of the freeway from the 605 Freeway to Costa Mesa at an estimated cost of $1.7 billion.

Caltrans is exploring the possibility of allowing vehicles with two or more occupants to ride free in the toll lanes, but a final decision has not been made.

The agency expects the bulk of project funding — $1.3 billion — will come from the county’s half-cent sales tax. But it’s unclear how the remaining $400 million will be raised.