The railroad confirmed the start of the run Monday and said the timing coincided with historically lighter rail volume over the US Fourth of July holiday.

The focus of the work will be on key routes between Shelby in Kentucky and Spartanburg, South Carolina, as well as Bostic to Monroe, North Carolina.

CSX said the work would take 18 weeks during busier times of the year, but the accelerated timeline was achieved by temporarily rerouting traffic on its main line in portions of three southeastern states to allow uninterrupted time for upgrades and repairs.

About two-thirds of CSX's system production teams and division engineering teams, signal teams and bridge forces are involved in what the company has referred to as the “July Jamboree”, with work to include the installation of more than 64,000 cross ties and 150,000 linear feet of rail, smoothing and shaping track roadbed.

Crews will also ballast over 40 track miles and upgrade road crossings.

The jamboree is part of CSX's $2.3 billion capital spend for 2013, which had been designed to help enhance its network in advance of increased demand for freight transportation services.

That demand is projected to increase by more than double nationwide by 2040, according to the United States Department of Transportation.

“Thanks to our dedicated employees, we're able to complete an incredible amount of work, while minimizing disruptions to our customers, to keep rail traffic moving safely and reliably," executive vice president and chief operating officer Oscar Munoz said.

“The maintenance jamboree is a prime example of the investment and effort we dedicate to ensuring that the nation's critical rail transportation network is ready to safely meet the country's growing needs while providing terrific benefits to our environment and our economy.”

CSX links more than 240 short-line railroads and more than 70 ocean, river and lake ports with cities and towns.