Flatiron, as managing partner of a joint venture, was responsible for the $24.7 million bid-build contract on the first phase of the Sorrento to Miramar Double Track project that comprised of 1.5 miles of new track, including crossovers and turnouts, parallel to the existing line from south of Sorrento Valley Boulevard to east of Interstate 805. The project was the first of two construction phases that helps speed passenger and freight rail services by straightening the slowest, steepest, and highest curve territories of any segment on the Los Angeles-San Diego-San Luis Obispo (LOSSAN) rail corridor. This stretch of single track between Sorrento Valley and Miramar Road caused a significant bottleneck to rail traffic. Due to the sharp curves and steep grade, train speed was restricted to 25 miles per hour. The project improved schedule reliability by increasing train speeds and allowing passenger and freight trains traveling in opposite directions to pass each other.

Flatiron demolished and replaced a 1940s era wooden trestle with a new 140-foot long double track bridge. This steel bridge was built on cast-in-place abutments and founded on driven steel pipe. To straighten the curvature of the current track alignment, crews constructed ten retaining walls—five different types due to varying geologic conditions—and embankments. This required working closely with SANDAG and their designer to construct the walls and new embankments while maintaining existing rail traffic and minimizing encroachment on neighboring properties. Special track work and signaling was also installed along the route.