While Los Angeles is widely known for its car-centric culture, an effort is underway to expand reliable public transportation for the city. This expansion will not only bring increased access and benefits for the communities served but will also reduce congestion and carbon emissions by providing an alternative to single-occupant vehicles.
A key part of this effort is the major expansion of the Metro rail system in Los Angeles, including the K (Crenshaw/LAX) Line project. The project will connect the E (Expo) Line via the Crenshaw Corridor through Inglewood to the C (formerly Green) Line near Los Angeles International Airport (LAX). This 8.5mi light rail expansion includes nine new stations, seven of which opened in 2022.
Arup supported lead designer HNTB in the delivery of this design-build project, providing a broad suite of multidisciplinary services including geotechnical and tunneling, tunnel ventilation, fire and life safety, structural, mechanical, electrical, and plumbing engineering for the underground stations. The Arup team also contributed civil and structural engineering for bridges connecting to the existing C Line.
8.5mi of new light rail track
200,000ft³/mintunnel ventilation fans
1,030 ftelevated guideway structure
Innovative digital coordination
To support the delivery of the underground portions of the K Line, Arup provided structural, mechanical, electrical, and plumbing engineering as well as ventilation and fire and life safety for the three underground stations and underground guideway sections. Using an innovative application of 3D modeling, we aided in the coordination and design of this complex transit project, as the modeling allowed for multidisciplinary alignment and stakeholder visualization to generate significant time and space savings.
At the time of design for the underground stations, 3D BIM techniques were not common in the infrastructure sector. We encouraged the use of Revit as the communication tool of choice, which allowed for review of several arrangements for the relocation of utilities and services, verification of structural designs, meeting of fire and egress design requirements, and flexibility for changes based on client needs. Our work on the project saw one of the first uses of Revit 3D modeling for a project of this type — a practice that is now seen more often in infrastructure projects.
Cost-saving tunnel ventilation solution
At the underground stations, the primary focus for the design of the guideways is to create a safe environment for passengers in the event of an emergency. Arup used computational fluid dynamics (CFD) analysis to model the train and tunnels to optimize the design while verifying the design of the ventilation systems to achieve safety approvals.
Ventilation systems are typically designed for the unique elements of stations, platforms, tunnels, and crossover exits. Arup proposed an optimized exhaust solution that consolidated these systems into an integrated tunnel ventilation plant for each underground station. Integrating station and tunnel ventilation systems resulted in savings in the excavation of dedicated fan plants serving either tunnels or stations. Additionally, our team provided commissioning and air flow performance testing to confirm that the performance criteria were met under normal, emergency, and congested operations. Our ventilation approach has now become an industry standard and was incorporated into subsequent Los Angeles Metro design criteria.
Dozens of engineers, designers, consultants, and experts on our multidisciplinary team have had a hand in delivering this project since Arup’s initial involvement two decades ago. It is rewarding to have played a major role in the expansion of critical transit infrastructure for the second largest city in the US. ” Andreas Raedle Principal, Americas West Rail Leader
Resilient structural engineering
The K Line involved the design and construction of many structure types, including bored and cut and cover tunnels, at grade structures, and viaducts. Supporting design-build contractor Walsh/Shea, Arup provided a variety of multidisciplinary services to assist with the alignment and coordination of requirements for connecting the new line to the existing Metro system.
As Los Angeles is in an earthquake-prone region, resilience to potential seismic events was an important consideration for the Crenshaw/LAX Transit Corridor. Our team conducted performance-based seismic design to inform our design of the underground station structures. Our engineers used the results from LS-DYNA, an advanced simulation software, to verify the design requirements for achieving operational continuity and safety in the event of an earthquake. Using LS-DYNA directly in combination with automation techniques, the Arup team was able to execute an efficient reinforcement design that accounted for a wide variety of earthquake scenarios. The use of this method for the seismic design of the Expo station provided about $3m in cost savings in the reinforcement of the station walls alone as compared to traditional methods. This approach is now required by LA Metro in future projects.
A key element of the Crenshaw/LAX Transit Corridor is the wye bridge connecting the K Line to the existing C Line. Unique in both its shape and function, this triangular junction is a concrete box girder bridge. The 1,030ft superstructure threads between the Interstate 105 viaduct above and Aviation Boulevard and Imperial Highway below. Arup provided structural engineering and bridge design for the wye connection, which was required to be compatible with the preexisting C-line viaduct built in the 1990s. Our design ensured that the foundation shafts supporting the structure were placed carefully to avoid existing structures and congested utilities. The wye connection is anticipated to open in 2023, completing the link between the Los Angeles Metro system and LAX.
Accessible transportation benefiting the community
The K Line expands the Metro system of Los Angeles, providing wider rail access to adjacent South Los Angeles neighborhoods and the airport. The improved connectivity will generate new economic opportunities for local businesses and expand transit access to the rich, diverse neighborhoods located in South Los Angeles. Importantly, the much-anticipated K Line provides greater regional connections for residents seeking more transport choices to access vital services such as healthcare and education as well as employment options.
Ahead of the construction of the new K Line, community members provided input on its design. In consultation with the community, the project incorporated underground tunnels along the Crenshaw corridor to minimize disruption to the community and local businesses both during construction and once operational.
The expansion of accessible public transit in Los Angeles benefits both people and planet. The K Line represents a step forward for relieving congestion on the roads, eliminating harmful carbon emissions from single-ridership vehicles, and promoting wider and more equitable access to the Metro system.