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Supporting safety with sophisticated software

Mott MacDonald was retained by LA Metro to assess the effect of a 19-megawatt train car fire in the Flower Street Grade Separation.

The new Expo Line ... will provide faster, more reliable public transportation and increase the capacity of the transit system in Los Angeles County.

LA Metro

Expo Line LRT Ventilation


In 2003, the Exposition Metro Line Construction Authority was created to award and oversee contracts for the construction of a 15-mile (24-kilometer) light rail transit line from downtown Los Angeles to the coast community of Santa Monica.

Phase 1 of the line, from downtown LA to Culver City, opened to the public in 2012. Phase 2, ending in Santa Monica, was expected to finish by 2015.

Phase 1 includes approximately 9 miles (14 kilometers) of double-track alignment and 11 passenger stations. From the northern terminus, where it shares track and two stations with the LA Metro Blue Line, it follows Flower Street, Exposition Boulevard, and Jefferson Boulevard with a southern terminus in Culver City.

The Flower Street Grade Separation is a below-grade section 2,500 feet (762 meters) long, between Flower Street and Exposition Boulevard. The northern end of the trench is 600 feet (183 meters) of covered tunnel, while the other end is open-roofed, with perpendicular street crossings at Figueroa Street and Pardee Way.

LA Metro wanted to ensure the safety of train crew and passengers in the event of a train car fire in the grade separation.


Mott MacDonald was retained by LA Metro in 2006 to assess the effect of a 19-megawatt train car fire in the Flower Street Grade Separation. Our contract was extended to include the testing and commissioning of the installed ventilation system

Mott MacDonald used computational fluid dynamics (CFD) to model the complete trench, including the atmosphere above it to include the effect of prevailing winds and of seasonal Santa Ana winds.

We used the egress analysis tool STEPS (Simulation of Transit Evacuation Pedestrian Movements), developed in-house, to quantify the time needed for evacuating passengers to reach a place of safety.

We determined that the ceiling openings alone would be inadequate to provide effective smoke control. CFD techniques were used to design a longitudinal jet fan system that would control smoke during a train car fire in the trench.


Mott MacDonald completed the project on time and within budget, helping to ensure safety in a key piece of the Phase 1 development.

According to LA Metro, “The new Expo Line is leading the way in regional efforts to shorten commutes and increase mobility. It will provide faster, more reliable public transportation and increase the capacity of the transit system in Los Angeles County. The line parallels the I-10 Freeway and provides an alternative to the freeway and major east-west arterials.”

Ridership on Phase 1 of the Expo Line is exceeding expectations, with about 27,000 daily riders. By 2030, 15 years after the entire line is completed, ridership is expected to reach 64,000 people per day. The completed line will have 19 stations serving destinations including USC, Exposition Park, the Mid-City Communities, the Crenshaw District, Culver City, West Los Angeles, and Santa Monica.

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