The ongoing expansion of Sound Transit outside of Seattle continues, with the latest move the awarding of a contract for the design-build project management of the Federal Way Link Extension south of Seattle. The contract initially covers the preconstruction period up to the award of the design-build contract.

And this is more than just any contract. At $1 billion, it will be Sound Transit’s largest design-build contract to date.

Awarded to South County Transit Partners, a joint venture of Mott MacDonald and SNC-Lavalin, the extension features a 7.8-mile addition of a regional light rail line with three elevated stations. The project will extend light rail service from the Angle Lake Station south of SeaTac to the Federal Way Transit Center.

New stations will be constructed near Kent Des Moines Road, South 272nd Street and the Federal Way Transit Center, all expected to open for service in 2024.

For Phase 1 of the project, South County Transit Partners will support the process leading up to the execution of the design-build contract. For Phase 2, the joint venture is expected to provide project management services during design and construction.

“This contract builds on the many years of solid design, project management and construction management services that Mott MacDonald has provided to Sound Transit,” Nick DeNichilo, president and CEO of Mott MacDonald in North America, said in a statement. “We are pleased to be joining SNC-Lavalin in the latest phase of transit development in the Puget Sound region.”

SNC-Lavalin will move into its first project for Sound Transit after recent work expanding the nearby SkyTrain system for Vancouver, B.C.

Services and responsibilities under the design-build project management contract include resident engineering, project controls and scheduling, change management technical support and inspection and quality assurance and quality control activities.

Future work at Sound Transit calls for extensions north to Everett, northwest to Ballard, east to Issaquah, Bellevue and Redmond and south to Federal Way and Tacoma.

Follow Tim Newcomb on Twitter at @tdnewcomb.