The Tramonto Slide
Location
Northbound State Route 1 (Pacific Coast Highway/PCH) at Porto Marina Way, ¾ miles north of Sunset Boulevard, in Castellammare (the city of Los Angeles).
The Slide
The Tramonto Slide is approximately 3 acres in size on the north side of the Pacific Coast Highway. Elevation changes almost 300 feet from the PCH to Tramonto Drive.
Background
The slide area referred to as the “Tramonto Slide” is much larger than the portion visible on the highway. It is approximately three acres in size and has been moving intermittently since the 1930s.
The Tramonto Slide is a deep-seated rotational landslide. Rotational landslides occur along a curved or spoon-shaped surface. There is often a toe of displace material. Rotational slides often occur because the internal strength of the material is overcome by its own weight. They are usually composed of relatively loose or unconsolidated material. Water has a significant influence.
Deep-seated landslides are typically much larger than shallow landslides, are often slow moving, and can cover large areas.
The most recent slide activity originated outside of state/Caltrans right of way, caused by a storm in early February 2024, and further saturated by additional storms in February and March 2024. The slide encroached onto Caltrans right of way, blocking the northbound right lane of two. Caltrans engineers are regularly monitoring the Tramonto Slide.
A joint study was done in 2010 by Caltrans and the City of Los Angeles, one of the property owners. The study documented the history of the slide and recommended that long-term repairs start from the top of the slide.
After the most recent slide incident had dried out for several weeks, the Caltrans Geotechnical Division determined the unstable nature of the slide prevents Caltrans from removing the debris from the northbound right lane of the highway near the toe of the slide and that repairs still need to start from the top of the slide, which is outside of Caltrans’ jurisdiction and right of way. Once reopening the right lane was ruled out, Caltrans moved forward with a plan to create an additional northbound lane by reconfiguring the remaining lanes.
Research by the Caltrans Right of Way Division has determined that most of the property parcels in the slide’s land mass above the PCH are privately owned and some are owned by the city of Los Angeles. Once the slope has been stabilized from the top, Caltrans can continue with repairs at the bottom of the slide.
A permanent resolution to the Tramonto Slide area must be determined through communication with the owners of the property outside of Caltrans’ right of way. Long-term mitigation may require construction of infrastucture on private property, including multiple retaining walls. There is no estimate of when a mitigation plan will be established. Caltrans is communicating with the city of Los Angeles on the issue and both parties agree that a new study is required to determine the current status of the slide. A study will require securing and reviewing mutliple core samples from the slide.
The Lane Closure
Since the slide is too unstable to clear the dirt from the northbound right lane, Caltrans realigned lanes on the Pacific Coast Highway to create a second northbound lane. There was no additional space in the median to create another lane. All northbound and southbound lanes were shifted towards the shoreline to create space for a second northbound travel lane that allowed the safe and smooth flow of traffic.
Construction included removing the existing curb along the southbound shoulder; removing existing pavement delineation, markers, and markings; realigning lanes around the slide area; grinding; repaving; restriping; installing signs; and placing k-rail at the toe of the slide.
The additional northbound lane was opened to traffic the morning of Thursday, May 30, 2024. The speed limit through the zone with realigned lanes has been temporarily reduced to 35 m.p.h.
Contact Information
Marc Bischoff
Public Information Officer
Caltrans – District 7
Marc.Bischoff@dot.ca.gov