I just learned of this:
If I understand correctly, as part of the Hwy 121 extension, the Hulen, and Bryant-Irvin bridges will come down over the Trinity Trails.
A new bridge - with Bicycle and Pedestrian access - will be built! The Bike/Ped access will be suspended below and connect to Trinity Trails! 
More from City of Fort Worth public release:
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Clearfork Main Street Bridge Design To Be Unveiled
The City of Fort Worth will unveil the final design for the Clearfork Main Street Bridge at an open house from
6:30-8:30 p.m. Aug. 6 (Thursday) at the Fort Worth Botanic Garden Center, 3220 Botanic Garden Blvd.
Exhibits about the bridge and plans for the surrounding area will be on display, and there will be a brief presentation in the auditorium. City staff and members of the design team will discuss the bridge.
The 1,800-foot roadway and bridge will connect Stonegate Boulevard to the planned Clearfork Main Street in southwest Fort Worth, linking Hulen Street to Bryant Irvin Road and the Southwest Parkway. The bridge will carry four lanes of traffic across the Trinity River. A separate pedestrian crossing will be suspended from the bridge to accommodate foot and bicycle traffic.
The pedestrian level will feature eight overlooks, four on each side. The design includes trail links on both banks of the river.
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