Big pieces of a wooden railroad trestle splashed into the San Elijo Creek during the first week of October, as workers demolished the 1944 bridge to make way for a new link in the chain of transportation projects underway along the 60-mile North Coast Corridor.
The disappearing trestle paralleled a new concrete railroad bridge that began carrying trains a few weeks ago, part of a $76.8 million project that adds a second set of tracks for 1.5 miles across the lagoon and into the Cardiff area of southern Encinitas.
Planning for the project began in 2011. Construction started in February 2017 and is expected to finish early next spring.
Other separate, but related efforts underway at the San Elijo Lagoon include building a wider, longer Interstate 5 bridge, and the $100 million environmental restoration of the entire lagoon, something planned for more than 20 years and expected to finish in 2020.
“These projects take intense environmental studies, studies of the birds, the fish, and the cultural resources,” said Bruce Smith, a principal engineer for the San Diego Association of Governments, the regional planning agency.
Doing multiple projects at once promotes efficiency in planning and construction, saves time and money, and lessens the inconvenience for residents and travelers, he said.
The new railroad crossing is assembled from pre-stressed, pre-cast sections of concrete made in Bakersfield and designed to last 100 years, Smith said. The sections can be replaced if damaged, and the entire bridge could be removed from its pilings and lifted to a higher level if, for example, sea-level rise proves to be greater than expected in 50 or 60 years.
In addition to being more durable and longer-lasting, the new bridge has fewer support pilings in the water, which is an environmental benefit to the lagoon and its wetlands.
Scientists planning the lagoon restoration studied all three bridges crossing the lagoon — Highway 101, the railroad and Interstate 5 — to determine the best ways to improve the water circulation needed for a healthy habitat.
The railroad trestle’s thicket of support pilings, nearly 100, restricted water flow beneath the bridge, said Doug Gibson, executive director of the San Elijo Lagoon Conservancy, which is the lead agency on the restoration.
“Kelp would get wrapped around it, which decays and leads to other issues,” Gibson said.
With fewer pilings in the water, less vegetation and debris can get caught under the bridge and water flows more freely.
The new railroad bridge is about the same length as the old trestle, which replaced the original one built about 1880.
Building a longer bridge would do little for water circulation and would not have been practical because the railroad is so close to the Highway 101 bridge, Gibson said.
Greater environmental benefits will be gained by making the Interstate 5 bridge longer, the studies showed. As a result, the new freeway bridge will be almost twice as long as the old one.
The San Elijo railroad bridge is part of an effort by SANDAG, Caltrans, and other state and federal agencies to double-track the entire coastal route from San Diego to the Orange County border.
Coaster commuter trains, Amtrak passenger trains, and BNSF freight trains use the route.
Double-tracking allows trains to pass each other. That improves the speed and reliability of existing rail service and makes room for more trains as the area’s population continues to grow.
“If they can’t pass, they have to wait to clear a single-track area,” said Jim Linthicum, SANDAG’s director of mobility and management.
“As we add more and more trains, if something happens and one is off schedule by a couple minutes that is going to mess up everything,” he said. “We want to have regular service that people can count on.”
So far, about two-thirds of the entire San Diego County route has been double-tracked.
Additional double-track projects already under construction or in design and environmental study stages should take the route to three-quarters complete, Linthecum said.
Construction of each one generally takes 18 months to two years. The goal is to double-track 94 percent of the route by 2035, and all of it by 2050.
A new double-track span crossing the Batiquitos Lagoon in Carlsbad is in the final design and permit stages. Construction there could begin in late 2019 if money becomes available.
One of the most difficult spots to double-track on the route is in Del Mar, where the single set of tracks follows the edge of the bluff. On one side is a cliff down to the beach, and on the other side are ocean-view homes. That leaves no room to build more tracks, and less room every year for the existing ones as the bluff erodes.
A tunnel appears to be the most likely solution, though no route has been chosen, and much work is needed before the decision is made. Initial estimates show a tunnel will cost billions of dollars, and the money is not available.
The entire North Coast Corridor program, with rail, freeway, environmental and other mobility projects, is expected to cost $6 billion. The funding comes from a combination of federal, state and local sources including the half-cent sales tax known as TransNet approved by San Diego County voters.
-- Phil Diehl is a reporter for The San Diego Union-Tribune.