While Los Angeles is widely known for its car-focused culture, an effort is underway to expand reliable public transportation for the city, increasing access for the communities served while reducing congestion and carbon emissions. A key part of this effort is a major expansion of the Metro rail system in Los Angeles, including the K (Crenshaw/LAX) Line project: an 8.5 mile light rail expansion including nine new stations.

Arup supported lead designer HNTB in the delivery of this design-build project, providing a broad suite of multidisciplinary services including geotechnical and tunnelling, fire and life safety, structural, mechanical, electrical, and plumbing engineering for the three stations located underground. The Arup team also contributed civil and structural engineering for bridges connecting to the existing C Line, to which the new line connects.

The new K Line expansion provides 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, providing access to healthcare, education and employment options, and was designed with input from the community to minimize disruption.

Building information modelling (BIM)

Using an innovative application of 3D modelling, Arup aided in the coordination and design of this complex transit project, with multidisciplinary alignment and stakeholder visualization to save time and space.

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.

Tunnel design

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, which limited 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.

Seismic design

Los Angeles is in an earthquake-prone region, so resilience to potential seismic events was an important consideration. 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.

Bridge design and engineering

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 1,030-foot 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.