No room to widen that highway? Start digging:
Three massive [tunneling] projects are under study in Southern California, each dwarfing any of the nation’s 337 underground roadways, including the 2.6-mile tunnel in Boston’s infamous “Big Dig,” the most costly public works project in U.S. history: Ã¯ Congress recently approved $2.4 million to study a five-mile, $2-billion tunnel that would help link the Long Beach and Foothill freeways in Pasadena and South Pasadena, and keep 100,000 cars a day off city streets. Ã¯ For Orange and Riverside counties, Congress set aside $16 million to study a 12-mile tunnel that would connect fast-growing commuter towns in the Inland Empire to jobs on the coastal plain. Buried beneath Cleveland National Forest and projected to cost from $3.5 billion to $5 billion, it would be the second-longest in the world Ã¢â?¬â?? after a 15.2-mile project in Norway. Ã¯ A complex of tunnels and surface highways under study by the city of Palmdale would slice 23 miles directly though the San Gabriel Mountains from the Antelope Valley to Glendale, cutting the commute in half. It could cost $3.1 billion or more. While some policy makers remain skeptical, others say engineering breakthroughs in Europe and Japan have made tunnels faster to build and more affordable Ã¢â?¬â?? especially where real estate prices have pushed the cost of new freeways skyward.
Article here. Sydney and Melbourne are also big into the tolled variety of tunneling. As this Reason study point out, tolled tunnels could work in California too:
[A] toll tunnel linking Palmdale with Glendale would dramatically shorten the commute time to Pasadena and downtown LA, while also paving the way for Palmdale Airport to attract major airline service. With a cost of $3 billion, toll revenues would cover all of the costs if the project was completed in two phases, or 83 percent of the costs if built all at once.
Going with a long term contract, in which a private partner assumes more risk, can also help sidestep the dreaded “Big Dig Syndrome.”