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California Incline Bridge and Idaho Avenue Pedestrian Overcrossing Now Open in Santa Monica, California

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T.Y. Lin International (TYLI), a globally recognized full-service infrastructure consulting firm, announces the completion of two infrastructure projects in Santa Monica, California: the new California Incline Bridge and the Idaho Avenue Pedestrian Overcrossing (POC). A 750-foot-long post-tensioned concrete slab bridge, the California Incline Bridge begins atop the bluff slopes of Pacific Palisades Park and carries vehicular traffic, pedestrians, and bicyclists down to the Pacific Coast Highway at the base of the bluffs near Santa Monica State Beach. The bridge replaces a series of deteriorating, seismically-deficient sidehill viaduct structures built in 1930. The Idaho Avenue POC replaces the former California Incline POC constructed in 1957. An aesthetic, curving structure with signature V-shaped pier, the replacement POC emerges seamlessly from the historic Idaho Trail and spirals down to connect to the new multiuse bicycle/pedestrian path constructed for the California Incline Bridge project.

TYLI served as bridge designer on the California Incline Bridge, working closely with the City of Santa Monica, the California Department of Transportation (Caltrans), and Wallace, Roberts and Todd (WRT), the Prime Consultant. The firm also oversaw traffic and electrical engineering, geotechnical engineering, hazardous material testing, and surveying. For the Idaho Avenue POC, TYLI served as Prime Consultant and provided concept alternatives analysis, final bridge design, plans, specifications, and estimates (PS&E), and construction support for the overcrossing and improvements to the Idaho Trail.

“T.Y. Lin International is honored to have worked with the City of Santa Monica and Caltrans to deliver two iconic structures,” said Mark Ashley, P.E., TYLI Senior Vice President and West Region Director. “The California Incline Bridge and the Idaho Avenue Pedestrian Overcrossing bring significant benefits to local residents, including improved safety, easy access to the beach, and breathtaking views of the Pacific Ocean. We are very pleased to have played a vital role in these important projects.”

About the California Incline Bridge:

Replacing a series of five sidehill viaducts, the new California Incline Bridge cuts through the steep shoreline slopes of Pacific Palisades Park and connects the intersection of Ocean and California Avenues at the top of the bluffs to SR-1/Pacific Coast Highway at the base. The bridge consists of a 750-foot-long cast-in-place, post-tensioned slab structure that has a total width of 52 feet to provide space for vehicular traffic and a barrier-separated bicycle/pedestrian path.

TYLI conducted a detailed type selection process to determine the best replacement alternative. This included taking into account the site’s environmental sensitivity, traffic impacts, constructability, structural performance, and project cost. The team also directed the work of surveyors to obtain a high-resolution LIDAR laser survey of the bluff cliff face.

The California Incline Bridge has been designed to accommodate the site’s corrosive marine environment and high seismic demands, including up to 20 feet of potential bluff erosion that could occur over its 75-year life span. Because the coastal bluffs constitute a protected resource, the bridge spans and 96 deep concrete piles were specifically located to minimize damage and erosion. Over 1,000 soil nails were installed in the slopes above the roadway to increase stability.

Structural design also called for the replacement of a 12-inch water main in the roadway and under the bridge, with bridge piles adjusted to avoid conflict with the waterline. Flexible high-density polyethylene (HDPE) pipe was used to allow replacement of the portion of the waterline under the bridge. TYLI also designed a temporary “high line” to maintain water service for residents during construction.

Aesthetic elements include the bridge railing, which replicates the historic balustrade railing of the original bridge, as well as a decorative overhang and corbels. LED lighting has been placed along the barrier-separated multimodal bicycle/pedestrian path. Additionally, the original bridge had a neon “Santa Monica” sign that was a landmark feature of the California Incline. The City of Santa Monica had the original sign refurbished and placed on a monument custom-designed by TYLI, once again giving the sign prominent exposure on the California Incline roadway.

About the Idaho Avenue Pedestrian Overcrossing:

Replacing an existing overcrossing, the Idaho Avenue POC extends from the Idaho Trail in Pacific Palisades Park and corkscrews tightly around the vertical clearance envelope of the California Incline roadway. Although TYLI’s design was driven by performance criteria related to site constraints, the sculptural profile of the overcrossing is reminiscent of a nautilus shell, facilitating its connection to the marine environment. Design challenges overcome included working with an existing trail with a steep 10% grade, space limitations over the California Incline roadway, the bridge location between steep, erodible cliffs and the City property line, and a large elevation drop between the popular trail and the roadway.

At the start of the project, TYLI provided a detailed structural assessment report that drove the City’s decision to replace the original structure. The design team then presented a variety of concepts and architectural renderings, of which three were chosen by the City for presentation to the general public. Following public selection, TYLI provided final engineering of the selected replacement alternative.

The primary architectural feature of the Idaho Avenue POC is the highly curved V-pier on the west side of the roadway, which provides a “window” to views of the Santa Monica Pier and the Pacific Ocean. TYLI worked closely with the contractor, providing 3D model files to enable the contractor to construct accurate forms for the V-Pier. The cantilevered deck of the bridge is accentuated by a transparent, LED-lit cable railing that minimizes view obstructions. TYLI also designed the bridge to transition gracefully from the trail grade to a code-compliant staircase that progressively widens on the decent.

Because the contractor for the California Incline Bridge was already working on the site, TYLI recommended that the City use the same contractor for the Idaho Avenue POC project. While this accelerated the timeline for the design process, the solution greatly reduced public inconvenience by utilizing existing road closures and detours. In addition, TYLI redesigned the Idaho Trail to minimize maintenance and erosion, which had been an ongoing problem for the City. This work included the design of a new drainage system for the trail.