Westside Purple Line Subway Extension, Section I


Los Angeles, CA


Los Angeles County Metropolitan Transportation Authority


$1.9 billion

As part of a joint venture, Traylor is constructing the $1.9 billion design-build of the Westside Subway Extension, Section 1, in Los Angeles. This is the first of three projects to extend the Purple Line from Wilshire Center to Westwood.

This project will add 3.92 miles to the Purple Line, beginning at the Wilshire/Western Station. The twin tunnel alignment will travel beneath Wilshire Boulevard, and underground stations will be constructed at Wilshire/La Brea, Wilshire/Fairfax, and Wilshire/La Cienega. The tunnels, mined by two Herrenknecht Tunnel Boring Machines (TBMs), will be 35,750 linear feet long with an inner diameter of 18 feet, 10 inches. The project also includes train control and signals, communications, traction power supply and distribution, and fare collection systems.

The largest and most complex of the three major excavations was La Brea station, which is 1,000 feet long, 65 feet wide, and nearly 80 feet deep, located down the center of busy Wilshire Boulevard. The work was also on the critical path, as it was the location from which the TBMs were launched.

At the Fairfax Station, near the La Brea Tar Pits, the presence of methane and hydrogen required an extra-large, extra-robust ventilation system operating 24 hours a day to remove contaminated air. Because of the risk to archaeological finds, all excavation at this site took place six inches at a time; the excavator ‘combed’ through a layer while the on-site paleontologist examined for fossils.

Hand mining done under hyperbaric conditions was needed on this project due to groundwater entering the tunnel and creating pressure levels higher than regular atmospheric pressure, similar to those found in an underwater dive. Ballard Marine Construction provided hyperbaric chamber operators, compressed air workers, and a medical team to oversee work in the cutterhead when water ingress forced the team to apply air pressure.

Elsie and Soyeon, the project’s twin TBMs, are supported by a complex conveyor system critical to meeting Traylor’s traditionally high levels of TBM productivity. Traylor’s underground group worked closely with Robbins to design a conveyor system for both tunnels that could make the complicated trip up and out of the south shaft. The one-of-a-kind conveyor system utilizes four types of belts and a three-story vertical storage cassette.