SANTA CRUZ >> To deliver an electric passenger rail system in Santa Cruz County capable of gliding above the many creeks, rivers and bustling roadways, will require the replacement of dozens of bridges at a price tag that nears $1 billion.

Staff with the Santa Cruz County Regional Transportation Commission and hired engineering consultant HDR reported in a public information session Wednesday that 28 of the 33 bridge structures within the commission’s 22-mile Zero Emission Passenger Rail and Trail Project will need to be replaced for a viable system along the Santa Cruz Branch Rail Line. The five structures that will remain will need repair and retrofitting work, planners said.

In all, the bridge replacement and rehabilitation effort is estimated to cost $980 million and the initial estimate does not include non-rail bridge infrastructure including trail segments, stations, retaining walls, fencing or alignment shifts.

“Most of the existing railroad bridges were originally installed by Southern Pacific Railroad as far back as the early 1900s,” said Peter Graff, a senior project bridge engineer with HDR. “We looked at the various span types along the line, which included steel spans, concrete spans, timber bridges and some steel trusses.”

One of the factors necessitating these replacements is an effort to bring the essential components of rail infrastructure up to an industry weight-bearing standard known as Cooper E80. The E80 design load standard, meaning the heaviest locomotive loads are 80,000 pounds per axle, applies specifically to active freight rail lines, of which the Santa Cruz line is one.

While commuter train load standards typically range from E40 to mid E50s, designing the crossings to the lower standard would only marginally reduce project costs and limit the lines’ ability to meet potential future demands of freight service, according to a staff report on this issue from last April. Additionally, the Branch Rail Line is included within the California State Rail Plan and the E80 designation, according to the report, and will preserve the ability of the rail line to integrate with the state’s plan while also ensuring the local agency remains competitive for future state and federal grant funding opportunities needed to deliver the local project.

“Why we’re doing that — designing for freight loading — is the ability to align with the State Rail Plan and to maintain connectivity with the national freight network,” said Graff. “But what that also means is we can of course handle passenger trains.”

Other features considered during the bridge evaluation process were adequate clearances above and beside roadways, and span resistance to hydraulic flow rates near drainages.

Graff said the engineering teams are considering six varieties of replacement spans or bridges including prefabricated concrete, rolled steel beam, steel deck plate girder, steel thru plate girder, steel deck truss and steel thru truss. Each option has its benefits and drawbacks including cost, longevity, maintenance and resistance to coastal weather and impacts.

Graff explained that one variety of existing bridge infrastructure that his team quickly realized would need to go were the timber bridges, a high concentration of which are located in South County, with some that were constructed more than 120 years ago.

The proposed passenger rail project extends from Pajaro Junction in North Monterey County to the Natural Bridges area in Santa Cruz. Under direction from the agency’s voting board, the commission staff has been hard at work since late 2022 developing a concept report that will provide a detailed analysis of the project’s engineering, environmental and financial costs. These latest findings about the bridges included within the project are part of that concept report effort.

After initially forecasting its release for early 2025, the commission’s Executive Director Sarah Christensen recently announced that the final report is now expected to come in the fall. The delay is meant to provide more time for community input, engineering work and understanding of the future funding landscape.

In the weeks and months ahead, Graff said the engineering team will continue with track designs, geotechnical engineering, bridge foundation types, clearance requirements, layout drawings and hydrologic openings over drainages. When that work is complete, staff will refine its cost estimates and summarize it for the commission.

Commission staff said much of the bridge infrastructure information will once again be shared with the transportation commission at its March 20 meeting and various stakeholder engagement events will continue throughout April and May.