A New Model for Integrated Planning in Transportation, Climate Resiliency, and Habitat Restoration

author list icon

This Program Allows for Long-term Planning of both Transportation and Environmental Projects in the California Coastal Zone, and Provides an Opportunity for Significant Advancements in the Corridor’s Climate Resiliency.

Project Summary

The Public Works Plan/Transportation and Resource Enhancement Program (PWP/ TREP) is a $6 billion, 40-year infrastructure plan in the California coastal zone that incorporates sea level rise planning and habitat restoration into a program of multimodal transportation improvements through the year 2050. The PWP/TREP is focused on the 27-mile North Coast Corridor, which serves as the northern gateway to San Diego County and provides access to its extensive coastal resources, including world-renowned beaches, lagoons, and upland recreation areas (see Figure 1). A joint product of the California Department of Transportation and the San Diego Association of Governments, the PWP/TREP contains a broad suite of freeway, rail, transit, bicycle, pedestrian, and environmental projects aimed at improving both mobility and sustainability. Major projects include:

  • Construction of two Express Lanes1 in each direction on Interstate 5 (I-5);
  • Double-tracking the San Diego segments of the Los Angeles-San Diego (LOSSAN) rail corridor;
  • Construction of over 30 miles of new bicycle and pedestrian facilities;
  • Replacement of multiple freeway and rail bridges crossing the corridor’s six coastal lagoons; and
  • Large-scale restorations of two coastal lagoons, plus the preservation and/or enhancement of numerous other habitat areas.

A New Model for Integrated Planning

Managed by Parsons Brinckerhoff (now part of WSP | Parsons Brinckerhoff) with substantial contributions from environmental consultant Dudek, the PWP/TREP has established a new precedent for long-term infrastructure programs in California. Its comprehensive approach allows for better long-term planning of both transportation and environmental projects, and the integration between the two types of projects provides opportunities for synergy and impact minimization that otherwise would not occur.

A Phased, Constrained Approach Ensuring Broad Benefits

The California Coastal Commission’s unanimous support for the PWP/TREP stemmed largely from the assurances provided by the implementation plan. Rather than contemplating a freeway expansion by itself, the PWP/TREP divided the freeway project into 10-year phases and then tied each phase to major rail and transit improvements, numerous bicycle and pedestrian projects, and a comprehensive suite of environmental measures to preserve and enhance sensitive coastal habitat and improve coastal access. This assures the Coastal Commission and the public that all multimodal and environmental components will be implemented at the same pace as the highway improvements.

San Diego map north coast corridor integrated planning transportation climate resiliency habitat restorationFigure 1– San Diego’s North Coast Corridor. (Graphic: Southwest Strategies) San Diego map north_coast_corridor integrated planning transportation climate resiliency habitat_restorationFigure 2– The original I-5 Bridge over Batiquitos Lagoon utilized substantial fill, artificially narrowing the lagoon channel and creating impacts to both wetland habitats and neighboring properties. (Photo: California Department of Transportation)

To further reduce impacts, multimodal projects in the same location—such as rail and highway bridge replacements in the same lagoon—are planned for concurrent construction. Additionally, every project will be required to comply with a comprehensive list of conditions and implementation measures that were specifically crafted by the lead agencies, the Coastal Commission, and the WSP | Parsons Brinckerhoff/Dudek team to protect and enhance sensitive resources.

Planning for Resilience

In addition to being a transportation lifeline serving both regional and international users, the North Coast Corridor is also an environmentally sensitive area. Both the I-5 freeway and LOSSAN rail alignments are located very close to the coastline, crossing six coastal lagoons and numerous sensitive habitat areas.2 A total of eight lagoon bridges—including some wooden rail trestles that are over 100 years old—are slated for replacement as part of the freeway and rail capacity enhancements programmed in the PWP/TREP. The program therefore provides corridor planners with a tremendous opportunity to make significant advancements in the corridor’s climate resiliency and overall environmental health.

Designing for Sea Level Rise and Erosion

The new lagoon bridges are being designed in accordance with the PWP/TREP’s sea level rise risk assessment, a technical analysis which was undertaken to assess all lagoon sites for future flood risk, and to verify that the planned bridge freeboards were consistent with current projections of sea levels and flood events likely to occur in the future.3

Given its 40-year implementation timeframe, the PWP/TREP also incorporated flexibility for changes, directing the future re-assessment of sea level risks at the later-phase bridge sites. With construction of some bridges not planned until 2030 or later, their design will be able to take advantage of the latest science on sea level rise and climate change.

The PWP/TREP also addresses shoreline erosion, a significant issue in the North Coast Corridor owing to its multiple waterbodies and sensitive coastal bluffs. Corridor-wide, the planned improvements will increase the treatment of runoff from impervious surfaces, and most lagoon and river mouths will benefit from the removal of culverts and other historic alterations to the shoreline’s natural state. Shoreline armoring will be permitted only for structures in the lagoons that have been proven to be in danger from erosion. Finally, one of the PWP/TREP’s largest single projects is the potential removal of the LOSSAN railroad tracks from the coastal bluffs in Del Mar, which is currently envisioned in the program’s final 10 year phase. The new rail alignment has not yet been decided, but if it does end up moving the tracks eastward, this will improve the long-term resilience of the LOSSAN corridor and reduce the need for future stabilization projects on the bluffs.

Optimizing Bridges for Lagoon Health

Constructed in the 1960s-70s, the existing freeway lagoon bridges sit atop substantial fill areas, which were originally aimed at reducing both the length and height of the required bridge structures (see Figure 2). Unfortunately, this also narrowed the lagoon channels and altered their natural behavior, creating a cascade of harmful impacts: to tidal flows, to water quality, to wetland habitats and even to the flood risks of surrounding properties. The planned bridge replacements therefore offered a golden opportunity to reverse these impacts.

A series of bridge optimization studies were commissioned for the PWP/TREP to examine the lagoons to determine the ideal widths and depths of their channels. These studies directly informed the design process, resulting in substantially longer bridges that will better convey tides and storm flows, helping to restore the lagoons’ natural functions and protect against future flood vulnerability.

The optimization studies utilized hydrodynamic models, calibrated with recent bathymetry data from the lagoons, to simulate various tidal and flood conditions. Using sensitivity analyses, the studies determined an optimal design length for each bridge: the point at which tidal range and flood conveyance are highly favorable, and any further increases in channel width and depth would only capture minimal benefit.

Restoring & Preserving Habitat

Accounting for the PWP/TREP’s large and varied suite of environmental enhancements and mitigations required intensive planning and analysis. To accomplish this, the WSP | Parsons Brinckerhoff/Dudek team worked closely with the Coastal Commission, the U.S. Army Corps of Engineers, and other agencies to develop a comprehensive and innovative Resource Enhancement and Mitigation Program (REMP).

The REMP lays out a detailed program of preservation, establishment, and restoration activities for the North Coast Corridor’s sensitive coastal resources which include two major lagoon systems and 220 acres of wetland and upland parcels. It also provides mitigation for the full suite of transportation improvements and accounts for 40 years’ worth of restoration and preservation activities.

An Unprecedented Approval

The Coastal Commission has a long history of opposing both freeway expansions and multi-decade permits within its coastal zone jurisdiction. But in August 2014, the Coastal Commission unanimously adopted the PWP/TREP, issuing its broad approval for all 40 years of North Coast Corridor projects.

The Coastal Commission’s support was unprecedented not just because it was a multi-decade approval that contained a major freeway expansion, but also because the PWP/TREP combined over 60 projects and three types of development permits—which typically must be analyzed and approved separately—into one omnibus document, saving the public substantial time and money.

The programmatic approval also greatly reduced regulatory risk by providing assurances to the lead agencies that the full program could be implemented. This will allow the San Diego region to plan and deliver the 40-year program in a coherent, coordinated fashion.


The North Coast Corridor PWP/TREP was an unprecedented, innovative document: a 40 year permit for a comprehensive transportation and environmental program of projects in California’s coastal zone. As this type of broad approval had never been granted before, it required a unique interagency process that evolved as the analyses and negotiations progressed.

From a sustainability perspective, the North Coast Corridor program will leave San Diego’s coastal environment healthier and stronger than any time in the past fifty years. By designing transportation projects for climate resilience and planning them together with environmental improvements, the PWP/TREP was able to capture mutual benefits while greatly reducing overall impacts—ultimately realizing more benefits for environmental health and sustainability than would have been possible without the transportation projects.

The PWP/TREP demonstrated that large multi-decade infrastructure programs can address concerns and provide benefits to satisfy even the most ardent regulatory agencies. The project has created a new model for public infrastructure programs in California, one that provides long-term assurances for mobility planning while simultaneously increasing the environmental health and resilience of local communities.


1Express Lanes are free for carpools and buses, but charge a toll to single occupant vehicles. The toll price varies based on real-time traffic levels and is intended to ensure free-flow conditions.

2In general, the rail alignment is located within 1,000 feet of the coastline, and is a mere 100 feet away in some locations. The freeway is slightly to the east, located approximately ¼-½ mile from the coast.

3The sea level rise risk assessment was led by engineers Moffatt & Nichol. Freeboard is defined as the clearance between the lowest point of the bridge superstructure (bottom of girder) and the design water surface elevation immediately upstream of the bridge.

back to top