Editor's note: This story has been updated to clarify the difference between SH 121 and Sam Rayburn Tollway. Work is being done along the tollway, not the frontage roads referred to as SH 121.

Work has begun on Sam Rayburn Tollway from Hardin Boulevard to US 75. Crews are excavating and removing materials in the center median in preparation for the addition of a new lane in each direction of the tollway. All work will be done in the median between concrete barriers.

The entire 26-mile project includes a new lane in each direction of the toll road from west of Denton Tap Road in Coppell to US 75 in McKinney. Construction is expected to continue through late 2021.

Timeline: January 2019-late 2021 (entire project) Cost: $200 million Funding source: North Texas Tollway Authority