Aliso Viejo, Calif. ? Traffic is so bad along the eastern rim of Los Angeles’ suburban ring that regional planners are considering the once unthinkable – an 11-mile tunnel through a mountain range in earthquake country.

Critics question the logic of building a multibillion-dollar project in a region so prone to earthquakes that an alternate proposal for a double-decker highway was deemed too dangerous. The tunnel would begin barely a mile from a fault that produced a 6.0-magnitude earthquake about a century ago.

“It’s absolutely absurd to have a tunnel 700 feet below ground in earthquake country,” said Cathryn DeYoung, mayor of Laguna Niguel and a vocal opponent. “I mean, would you want to be in that tunnel?”

Planners are due to make a decision in mid-November on whether to pursue the project.

The proposal for what would be the world’s second-longest road tunnel would create a new path between sprawling inland suburbs and Orange County, which has become one of Southern California’s fastest-growing job centers.

Such a project could cost up to $9 billion and take 25 years.

Transportation officials insist something drastic must be done to deal with the crippling traffic congestion between Orange and Riverside counties, which are separated by the 25-mile-long Santa Ana Mountains. Nearly 400,000 people commute into Orange County daily from four surrounding counties and nearly all of them drive.

California Highway 91, the only major road connecting Riverside County, where homes are more affordable, to jobs-rich northern Orange County carries 268,000 cars a day, nearly 50,000 more than it was built to handle. Officials expect that to increase over the next 25 years to nearly a half-million cars per day.

Howard Gottesman, 44, can spend 1 1/2 hours on Highway 91 to travel just six miles from his job as a property manager in Orange County to his home in Corona, just inside Riverside County.

“I call it the longest six miles in the world. It’s wear and tear on the car and it’s wear and tear on me,” Gottesman said. “They need to do something, whether it’s double-decking the freeway or tunneling under the mountains. We need relief.”

As currently conceived, the four- or six-lane tunnel would make up more than two-thirds of a 15-mile corridor connecting Interstate 15 with two toll roads in central Orange County.