In a bustling city anticipating 20-percent population growth over the next decade, San Diego residents eagerly welcomed the light rail transit (LRT) extension of the University of California (UC) San Diego Blue Line Trolley to provide reliable transportation along the congested Interstate 5 (I-5) corridor.

On Nov. 21, the $2.1 billion Mid-Coast project, an 11-mile double-track light rail extension of the UC San Diego Blue Line Trolley, officially debuted its public operations with a grand opening celebration.

“At a time when we are witnessing rapid population growth in this popular section of San Diego, the Mid-Coast Trolley Extension is arriving to provide critically needed public transit service along this corridor,” said Kimberly Jaskot, WSP USA project manager for design services during construction. “The project will provide an effective alternative to congested freeways and roadways for travelers and will result in fewer vehicle miles being traveled.”

As a key member of the project’s design team for more than a decade, WSP served as the project’s lead environmental and engineering consultant and the designer of record on behalf of the San Diego Association of Governments (SANDAG). WSP handled multiple responsibilities for the project, including environmental, planning, preliminary and final engineering, New Starts funding advisory services and design services during construction of the light rail extension operated by the San Diego Metropolitan Transit System (MTS).

The extension connects corridor residents with other Trolley lines serving Mission Valley, East County and South County. The Mid-Coast Trolley Extension offers a transfer-free ride from the U.S.-Mexico International Border and communities south of downtown San Diego all the way to the University Community area.

The project included the design and construction of eleven bridge crossings, nearly seven miles of at-grade alignment in or near existing railroad right-of-way, more than four miles of aerial viaduct structures, and nine stations – four at-grade and five aerial. Five of the stations will provide a combined 1,170 new parking spaces.

The Mid-Coast Trolley Extension features a one-mile-long, two-track viaduct along Genesee Avenue, which includes two elevated stations. As an arterial street, Genesee Avenue is critical for accessing the UC San Diego campus, residential housing, hospitals, a shopping mall, schools and businesses. Extended closure of the roadway was not an option.

“Understandably, one requirement for our design was to keep the major intersections along Genesee Avenue open and operational throughout construction,” said Vladimir Kanevskiy, engineering technical lead for WSP. “Full closure of the intersections was only permitted for a short period of time, and even then, only one intersection at a time.”

This requirement applied to six locations where precast girder spans crossed over live traffic. The original plan was for cast in place construction, but the approach was changed in order to minimize disruption to the community and those traveling along the roadway.

To address these conditions, the design team developed an innovative approach to splice the precast girders at the site. The spliced segments, which varied from 140 feet to 180 feet, were erected and placed on shoring towers during evening closures, minimizing impacts on the traveling public.

The resulting viaduct constructed within the median of Genesee Avenue is the first curved spliced precast U-girder LRT bridge in Southern California.

“Maintaining local traffic and minimizing impacts to the surrounding community were primary drivers of structure type and construction methods,” Kanevskiy said, adding that the techniques used on this viaduct will influence future designs in similar circumstances. “WSP’s experience with design of precast post-tensioned spliced girders is being considered on other projects where potentially significant traffic impacts during construction can be minimized.”

To ensure fair treatment of everyone potentially impacted by the project, an environmental justice analysis was conducted as part of the environmental clearance process. The analysis identified nine environmental justice communities within the Mid-Coast Corridor, five of which were within a half mile of the alignment. Additionally, six of the nine new stations are located in environmental justice communities.

“The analysis concluded that there would not be any disproportionately high and adverse impacts to environmental justice communities,” said Kristin Carlson, WSP project manager for environmental support.

The Mid-Coast Corridor Transit Project Refined Build Alternative Report determined that more than 60 percent of user benefits would accrue to low-income groups both inside and outside the corridor, thereby supporting equity goals. In addition, the Veterans Administration Medical Center Trolley Station would provide convenient access for veterans—disabled and otherwise—seeking medical treatment.

“There were a number of disadvantaged business enterprises supporting the project throughout environmental clearance, final design and design services during construction,” Carlson added. “Their input from environmental clearance through to construction was valuable in ensuring the project stayed on the right course.”

WSP played an integral role in coordinating major components of the project among various consultants working closely with SANDAG and its partners to advance the project through critical milestones. Construction along the 351-mile Los Angeles–San Diego–San Luis Obispo Rail Corridor (LOSSAN Corridor), the second busiest passenger rail corridor in the country, was one of those major components.

“The WSP design team developed detailed staging plans involving temporary track shooflies, multiple relocations of the Rose Canyon bike path, reconstruction of Rose Creek flood control channel, and construction of specialized retaining walls and a Rose Canyon LRT flyover structure,” Jaskot said. “All while maintaining 48 trains per day along this narrow rail corridor.”

The project also had to account for concurrent adjacent construction of the Rose Canyon Bike Path at various locations, the Rose Creek Channel reconstruction, and the new LRT flyover structure construction, as well as design modifications to freeways, streets and bike lanes at several locations to accommodate the guideway.

Adding to the challenge: The Mid-Coast Trolley Extension crossed the active Rose Canyon fault line.

To ensure the long-term safety of the extension, the design team performed an extensive subsurface investigation, which included physical borings and numerous geophysical techniques to accurately locate and assess multiple active tributary fault lines. Innovative structural design solutions were employed to allow for movement in the guideway superstructure to prevent unseating of girders during a seismic event.

Geotechnical observations conducted during the construction phase positively confirmed locations of the fault lines, which helped the team avoid design changes down the road caused by differed site conditions. This allowed the project team to maintain construction progress without interruptions.

“WSPs understanding of the project allowed us to execute amidst all of the challenges and changes,” Jaskot said. “A complicated progression of multiple construction phases was navigated successfully through meticulous planning and execution of the work alongside SANDAG.”

WSP provided grant procurement services, which aided SANDAG in securing a $1 billion Federal Transit Administration Full Funding Grant Agreement. The federal funding matched approximately $1 billion provided by TransNet, the half-cent sales tax administered by SANDAG to support transportation projects in the San Diego region. Once the project was fully funded, construction was able to begin in 2016. The project was completed on time and on budget.

Throughout the decade that WSP worked on the project, the environmental and engineering teams collaborated extensively to advance the project from planning and environmental clearance to construction.

“This collaboration meant that the design of the project from the start was able to avoid or minimize impacts to resources, minimizing the mitigation required,” Carlson said.

For example, Carlson said that during the permitting process, the environmental team coordinated with resource agencies and the design team to modify the design of project elements to minimize impacts to resources. The sequencing of construction for the channel, bike path, LOSSAN, and LRT tracks was also important to the environmental analysis.

“This project presented many unique technical challenges, including difficult geological conditions, utility conflicts, adjacency to active railroad and construction in an urbanized environment where impacts to businesses, schools and medical facilities had to be carefully mitigated as part of the design development,” Kanevskiy said. “We are grateful to have been part of a project team that was able to collaborate and successfully manage and overcome all of those challenges.”

“Public perception was largely positive for the project, and there was little to no opposition during the environmental clearance phase,” Carlson added. “It’s been rewarding to partner with SANDAG on the delivery of one of the largest infrastructure projects ever undertaken in the region and to help them achieve major milestones throughout environmental clearance and construction of such an important transportation project for the region.”

“The Mid-Coast project is one of the highest-priority transit projects ever undertaken locally, highlighting improved access to major employment, healthcare, education and cross-border opportunities,” Jaskot said. “It is an outstanding example of the value of partnership and collaboration.”

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