A Mission Valley West LRT vehicle, running on slab track, approaches a station.

In 1985 the City of San Diego’s Mission Valley Community plan directed the integration of land development and public transportation. The valley’s topography, the meandering San Diego River, and existing development limited the opportunities for building additional streets and highways. In 1997, after ten years of planning and just over two quick years of construction, San Diego was provided with the 6.1-mile (9.8-km) long Mission Valley West LRT. The new segment is now part of San Diego Trolley’s 25.2- mile (40.3-km) Blue Line, which also serves the Old Town Transit Center, downtown San Diego, South Bay communities, and the International Border at Tijuana.

Through the versatile use of concrete—aerial structures, track, platforms, canopies, and pavement—the Mission Valley West LRT successfully met its objectives: increase accessibility and mobility, protect the environment, conserve energy, and improve the quality of life. Concrete literally served as the foundation for new urban development in the Mission Valley.

The Mission Valley West LRT’s alignment required that 95% of the right-of-way be purchased. Earlier trolley projects were built at grade, on railroad rights-of-way or public rights-of-way in city streets. The city had negotiated development agreements with affected property owners in the 1980s that preserved or dedicated rights-of-way for the future LRT route. The route parallels the San Diego River and its flood plain, crossing the river at three locations. The route also had four highways crossings. There was also an earthquake fault line, which added an additional engineering challenge. The project included four at-grade and three elevated stations, and a multi-bay bus transfer area.

Construction contracts were divided into two equal segments: Morena and Stadium. Contractors were able to complete all underground utility relocations, environmental mitigation, ten bridges, and seven stations between June 1995 and the end of 1997, ahead of schedule.

Transit-oriented development (retail, residential, mixed-use) is still occurring along the alignment and adjacent to the stations.

Aerial Structures

Concrete aerial structures are a critical component of the expansion project.

Approximately 2.5 miles (4.0 km) of the 6.1-mile (9.8-km) long route are bridges and aerial track structures. Along the north side of the San Diego River, elevated structures keep the trolley well above the river’s flood plain. Between Fashion Valley Transit Center and Hazard Center Station, a graceful 0.75-mile (1.2-km) long bridge curves over State Route 163. At Qualcomm Stadium the track was again elevated to avoid traffic conflicts between light rail vehicles and automobiles in the stadium parking lot.

Section 2-7.7.2 Superstructure Materials of the LRT Design Criteria (published jointly by the Metropolitan Transit Development Board and San Diego Trolley Incorporated) states that “Concrete is preferred for maintenance, cost, and appearance, but alternatives in steel may be considered if they can be shown to be superior and cost-effective on a life cycle cost basis, including the costs of maintenance.” Consequently, all of the Mission Valley West LRT elevated structures are constructed of concrete.

Since the alignment also runs beside, and at some points crosses, an active fault line, design criteria were established for a maximum credible earthquake of magnitude 6.2. Foundations, substructures, and superstructures were all designed according to these criteria and the latest seismic standards from the California Dept. of Transportation. In lieu of ballast and ties, track rails were fastened directly to the concrete deck of the superstructure. This direct fixation (DF) track type offered significantly reduced dead loads on the structure, an especially important consideration in seismic regions. Rail/structure interactive forces—forces caused by providing continuously welded rail, special trackwork (turnouts, equilaterals, and crossovers), dynamic forces of the trolleys, structural dead loads, and seismic forces—required a complex structural design. Elevated structures are typically founded on concrete cast-in-place drilled-hole piles from 16 to 108 inches (400 to 2,750 mm) in diameter, sometimes at a depth of over 100 feet (30.5 m).

Cast-in-place prestressed box girders span across the Qualcomm Stadium parking lot.

Stadium Bridge Structure
The elevated section that runs through the Qualcomm Stadium parking lot is over 3,200 feet (975 m) long. The cast-in-place, prestressed concrete box girder has spans ranging from 100 to 132 feet (30.5 to 40.2 m), and is supported by 5-foot x 8-foot (1.5-m x 2.4 m) elliptical concrete columns. The columns here are anchored into 9-foot (2.7-m) diameter cast-in-place drilled-hole piles that have been embedded over 60 feet (18.3 m) into the ground. This structure is wider than at typical double track sections to accommodate pocket tracks located in both ends of the Stadium Station.

Stations

Station Character and Uniqueness
Different architectural treatments were used to develop character and uniqueness for the trolley stops at all seven stations of the Mission Valley West LRT extension. Architectural treatments also reflect commercial and residential structures surrounding the stations.

Station and platform areas are completely Americans with Disabilities Act (ADA) accessible, with ramps at all stations and elevators at elevated stations. Platform edges include tactile warning strips made with yellow-colored precast concrete. Before selecting precast, integrally colored concrete edge strips as the long-term solution, painted concrete and rubber panels were tried.

Fashion Valley Transit Center

Concrete substructure and superstructure elements are used exclusively throughout this transit system.

Owners of Fashion Valley Regional Shopping Center, San Diego’s largest shopping center, decided to expand in coordination with the coming of light rail. The trolley tracks and elevated station were located to conform with the expansion. A mid-level pedestrian bridge, provided by the shopping center, connects the station to a multi-level concrete parking garage.

At ground level, a 14-bay bus transfer area replaces a smaller facility on the other side of the shopping center, and provides elevator connections to the trolley tracks at the station’s top level. The agency’s standard is concrete pavement for bus pads, driveways, and other areas used by buses.

Hazard Center Station

Slab track is used extensively along the route.

Trolley tracks descend to grade level at the Hazard Center Station, which serves retail, hotel, entertainment, office, and residential uses. The station and tracks are located between Hazard Center Drive and Union Square, a new residential development. Union Square required a change order to the LRT construction documents as it came to life near the end of the design phase. Concrete flatwork for the passenger platforms and sidewalk areas is integrally colored in pinks and light natural hues, reflecting the colors used on the exteriors of the adjacent homes.

The vehicular entrance to Union Square is from Hazard Center Drive, crossing the trolley tracks at grade at the station’s east end (one of only two such locations on the alignment). The tracks are embedded in a concrete infill pavement that is colored black and impressed with a slate-like pattern. The color and pattern delineate the driveway from pedestrian areas and offer a formal entry for residents. For safety and noise reduction, the station and tracks are separated from the residences by a 6-foot (1.8-m) high pink-colored concrete wall topped in white.

Mission Valley Center Station
Eastwards from the Hazard Center is Mission Valley Center Station, which is located in the Park-in-the-Valley shopping development. The concrete pavement, inlaid with a striking sunburst design, leads pedestrians between the shops and the station. Done in pastels and earth tones, the walkway coordinates with the colors of the surrounding store walls.

Conventional cast-in-place concrete wall construction technology was combined with the latest formliner system to recreate the color and texture of natural rock at a fraction of the cost. Cobblestone-simulated formliners (also used at the Old Town Transit Center) were used for wall panels at the station. After the formliners were stripped, the concrete “cobblestones” were stained to replicate the colors and textures of natural stone.

Qualcomm Stadium Station

The Qualcomm Stadium station is constructed using graceful elements for the concrete platform canopy.

The final station stop heading eastward is at San Diego Qualcomm (formerly Jack Murphy) Stadium. The stadium is home to the San Diego Padres professional baseball team and the San Diego Chargers National Football League team, and holds more than 300 events each year. The stadium station is functionally designed to carry 6,000 people within 30 minutes after an event ends. An estimated 25,000 passengers (35% of those in attendance) rode the trolley to Super Bowl XXXII in January 1998.

The station was designed for large crowds by providing three platforms (two side and one center), connected to the stadium by a 125-foot (38-m) long concrete walkway. Pocket tracks accommodate 18 light-rail vehicles. The station’s award-winning architecture replicates that of the stadium’s by mimicking its light supports and upper deck with soaring concrete pillars and canopies. Arrangements have been made for the stadium parking area to be available for use as a transit park-and-ride lot as well.

Track Construction

Crosstie and Ballast Track

Prestressed concrete crossties are used for particular at-grade line sections.

Direct Fixation Track

Elevated structures incorporate the use of direct fixation track for durability and low maintenance.

In lieu of ballast and ties, the direct fixation track type was used to attach rail directly to elevated structures. The rail and fasteners are set on 22-inch (560-mm) wide reinforced concrete plinths keyed every 24 or 30 inches (600 or 750 mm) into the superstructure’s concrete deck. The plinths elevate the rail and fasteners from the deck for better drainage. Direct fixation track significantly reduces dead load on the structure by eliminating the ballast, thus making the bridge and its foundations lighter. DF track provides a smoother ride because it better retains the location of the rail, and smooth ride translates into reduced vehicle and track maintenance.

Tracks were embedded in cast-in-place concrete up to the top of the rail through at-grade station areas, allowing passengers to cross over the tracks to access all platforms. At elevated stations, precast concrete removable panels were used to accomplish this. The precast panels are removable for easy access to rail and fasteners for maintenance.

Wetland Mitigation
By selecting an alignment parallel to and crossing the San Diego River, 6.5 acres (26,300 m2) of environmentally sensitive habitat were needed for construction, or were otherwise adversely affected. To comply with environmental regulations the project team devised a 25-acre (101,200-m2) environmental mitigation site, providing more than the 3:1 replacement ratio required by the environmental permit. The land purchased had been the River Ranch Golf Course.

The mitigation site consists of riparian habitat, freshwater marsh, open water, and two islands. The concrete elevated structure that carries the tracks requires very low maintenance, which means minimal disruption to the wetlands. The natural habitat has already become a wildlife preserve supporting 33 bird species and a variety of plants and animals.

 
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