A new alternative was proposed in 2003 as an 4.5 - mile ( 7.2 km ) tunnel .
A new alternative was would cost $2.6 to $3.6 billion , with some expenses reimbursed by charging tolls .
A new alternative was proposed in 2003 as an 4.5 - mile ( 7.2 km ) tunnel and would cost $2.6 to $3.6 billion , with some expenses reimbursed by charging tolls .