A trench on the bluff is the newest idea proposed for protecting the railroad tracks along the eroding Del Mar coast.
Rerouting the tracks through tunnels has been the preferred long-term solution for years, but officials say digging a trench in place could be done faster and cheaper.
Another problem on the bluff is that the existing site is too narrow to build a second set of tracks, making it a choke point as the railroad is double-tracked from Orange County to downtown San Diego. So far, about two-thirds of the route has been double-tracked.
Any of the proposed new routes, or trenching the existing route, would create enough space to double-track. A similar situation exists on the coast of San Clemente and San Juan Capistrano in southern Orange County.
Four different routes through Del Mar have been considered for the tunnels — two that would take the tracks along Interstate 5 on the east side of town, and two that would go through Crest Canyon closer to the center of the small city. About five miles of track would be re-routed, with parts of it in tunnels as deep as 270 feet.
A fifth possible route would place trains in a trench up to 70 feet beneath Camino Del Mar, which is the main coastal thoroughfare, also known as Highway 101. The trench would be topped with steel plates to allow vehicles to drive on top of it. All five possible routes were outlined in a recent study by the San Diego Association of Governments, the region’s planning agency.
The newest option involves building a trench on the existing route across the Del Mar bluff, SANDAG principal engineer Bruce Smith recently told the North County Transit District board of directors. The transit district owns the tracks and controls train traffic on the 60-mile corridor from the Orange County border to the Santa Fe Depot in San Diego.
The straight-walled trench would be 1.5 miles long, up to 26 feet deep and 55 feet wide, with room for two sets of tracks.
“We could install pedestrian crossings and ramps down to the beach,” Smith said. Linear parks also could be built atop parts of the trench.
“That’s something to think about as we go forward in Del Mar,” he said.
Construction costs for re-routing about five miles of track and putting parts of it through tunnels range from $2.5 billion to $3.5 billion, depending on the route chosen. The cost of the trench is estimated at $300 million to $400 million.
SANDAG is about midway through a series of phased projects expected to stabilize the bluffs through 2050. Rerouting or trenching are proposed to safeguard the tracks further into the future.
The agency has spent about $18 million on stabilization projects to date, has projects costing $24 million in planning and design stages, and plans to spend about $64 million more on protecting the bluff-top route through 2050, Smith said.
— Phil Diehl is a reporter for The San Diego Union-Tribune