Perhaps no traffic bottleneck in Los Angeles County has frustrated transportation planners and commuters more than the Sepulveda Pass, where the infamous 405 Freeway connects the Westside and the San Fernando Valley.

The Metropolitan Transportation Authority plans to propose a radical step: Pushing a tunnel through the mountains that could accommodate a toll road and a passenger rail line.

The tunnel is one of nearly a dozen major transit projects Metro says it could build if voters approve a $120-billion tax increase proposal expected to appear on the November ballot.

Other projects include rail lines through the San Fernando Valley and southeastern L.A. County, as well as faster bus service on a handful of major corridors, according to two officials briefed on the plan. They spoke to The Times on condition of anonymity because they were not authorized to discuss the matter publicly.


The ballot measure would extend an existing half-cent sales tax for two more decades, and raise the county’s sales tax rate by an additional half-cent for four decades or longer. The measure, which needs a two-thirds majority to pass, would boost Los Angeles County’s base sales tax rate to 9.5%.

Some details have yet to be worked out, the officials said Friday, including the exact division of funding between new transit lines, Metro operations and repairs, and disbursements to municipal governments for local projects, such as paving potholes and painting bike lanes.

As envisioned, the plan would funnel about one-third of the $120 billion into full or partial funding for five new transit lines and at least six extensions of lines that are already built or under construction, the officials said.

The project list appears carefully constructed to gain voter support in all areas of the vast county, with rail lines, highway upgrades and other proposed improvements reaching communities as far-flung as Sylmar, Torrance, Artesia and Claremont.


“In terms of the order of these projects, what’s going to be at the beginning and what’s at the end, and how it’s all rolled out, that’s all being finalized,” Metro spokeswoman Pauletta Tonilas said Friday. “There’s been a tremendous amount of work that went into this, keeping in mind that this is a regional system for everyone in the county.”

She declined to comment on any specific projects until the list is released publicly later this month.

“What we’ve been saying is, everyone is going to get something, and no one is going to get everything,” Tonilas said. “And not everything can be built in the next 15 years.”

The construction plan could be transformative for traffic-choked Los Angeles County, which began building a modern rail system a generation ago, decades after other major cities. The plan would provide several critical north-south links in a rail network that runs largely east to west, in part because Metro could purchase abandoned rights-of-way for a deep discount.


But critics say the proposal could be a colossal headache for Metro, which sometimes struggles to manage the budget it has now. Despite major investments over the last decade, ridership has dropped on buses and trains. The widening of the 405 Freeway was completed years behind schedule. And the budget for a new rail connection through downtown Los Angeles has increased by $130 million, or 9%, before tunneling has even begun.

Little is known about what happens when a region faces a sales tax of 10% or higher, said Lisa Schweitzer, a USC associate professor in transportation and urban planning. Although Metro’s proposal would increase the county’s base sales tax rate to 9.5%, some cities — including Santa Monica, Culver City and Commerce — have higher rates.