Project officials for the $2.1-billion Mid-Coast Trolley in San Diego recently celebrated the halfway point of construction. The event was held at the construction staging yard near the Voigt Drive Trolley station, where workers gather for their morning briefings.

Led by the San Diego Association of Governments (SANDAG), the Mid-Coast Trolley project will travel in existing railroad right-of-way and alongside the I-5 Freeway, and extend trolley service from Santa Fe Depot in Downtown San Diego to the University City community, serving major activity centers such as Old Town, UC San Diego, and Westfield UTC. Construction, which will build nine new stations, began in fall 2016 and is scheduled to complete in late 2021.

The project will connect corridor residents with other trolley lines serving Mission Valley, East County, and South County. As an extension of the existing Metropolitan Transit System Trolley Blue Line, the Mid-Coast Trolley will offer a one-seat (no transfer) ride from the international border and communities south of Downtown San Diego all the way to University City.

“Not only is this project large in scale, but its impact on the San Diego region is bound to be monumental,” said SANDAG Board Chair and Mayor of Poway Steve Vaus in a news release.  “This is the largest public transit project in our region’s history.”

The project was designed by a team of SANDAG engineers with the assistance of WSP (formerly known as Parsons Brinckerhoff). Mid-Coast Transit Constructors (MCTC), a fully-integrated joint venture of Stacy & Witbeck, Inc., Skanska USA, and Herzog Contracting Corporation is building the project.

The trolley is being delivered through a construction manager / general contractor (CM/GC) methodology. MCTC was brought on to the project at the 65% design level and has worked side by side with SANDAG and the designer to conduct constructability reviews as design progressed to Issued for Construction (IFC) drawings. SANDAG says this delivery method improves the project’s ability to complete on schedule and within budget.

As can be expected, a job of this magnitude is not without challenges.

The project is being constructing an elevated guideway running down Genesee Avenue through one of the busiest areas of San Diego. Work involves having to utilize specialized trucks to transport 142 pre-cast girders, measuring up to 80 ft-long and weighing up to 95 tons, approximately 75 miles from Perris, CA.

“Transportation of the girders needs to be performed during off-peak hours, requiring careful coordination with California Highway Patrol,” says John Haggerty, PE, SANDAG’s project director. “Impacts to the surrounding community were reduced by approximately 9 months by switching to the use of pre-cast girders in lieu of cast-in-place concrete box girders, which are more commonly used in California. The challenge of having to complete this structure in such a highly urbanized area was further overcome by implementing a proactive public awareness campaign that included establishing partnerships with other public and private entity construction projects to disseminate information about traffic impacts.”

Another challenge was the existence of compressible soils just north of the San Diego River. This posed the potential for buildings adjacent to construction to settle, says Haggerty. “This challenge needed to be addressed during the design phase and ultimately required the use of lightweight cellular concrete as an alternative solution for fill material,” he says.

And then there was the issue of an earthquake fault running through Rose Canyon along the Mid-Coast corridor. Both light rail and commuter/freight rail bridges were designed for no collapse, despite the potential for a four to six foot displacement associated with a fault in the region.

The project is currently about 50 percent complete with upcoming work including construction of a new trolley underpass and construction of the Rose Creek flyover. The latter is where the trolley bridge will need to pass up and over the preexisting heavy rail that runs through the Rose Creek area to touch down on the west side of the alignment to prepare to cross over the I-5 Freeway.

Other ongoing work includes installing girders, pouring station decks, installing handrails, laying track, and installing all wiring and systems. Once construction is complete, testing will begin with the new trolley cars.

Once complete in 2021, the project is expected to have poured four million cu-ft of concrete, installed 27 million pounds of rebar, and laid 83 miles of railroad ties.