Other firms are helping boost capacity by modeling more efficient routing. AECOM used its proprietary RailOPS program to help Caltrans improve network rail operations in California, and several freight rail companies are examining the simulation platform, says Rachel Vandenberg, AECOM vice president.

As track-time windows shrink, contractors look for ways to be more productive and expedite construction. Some differentiate themselves by their ability to use high-productivity, specialized machines such as ballast regulators and grinding equipment, says Baker.

Levy says technology such as laser-guided track alignment equipment pushes productivity, but construction and maintenance still rely on manual labor. Railworks peaked at 2,700 workers in 2013 and boosted worker hours by 50% over the past three years, he adds.

Thanks to the expanded capacity, railroads are competing directly with other modes, such as trucking. U.S. port upgrades are bringing rail networks right up to the ships, streamlining bulk loading.

The combination of growth in intermodal and oil shipping means that railroad investment should continue at its current record pace, according to industry watchers. "It appears like they are each working right now to build some competitive advantage into their networks," Levy says. "Each railroad wants to provide a more comprehensive service."