http://www.dot.state.tx.us/tpp/hwy/sh/sh0121.htm
Quote
Minute Order 109187, dated 02/27/2003; DesLtr 01-2003, dated 04/04/2003
From SH 78 north of Bonham, southward to its junction with US 82; then concurrent southwestward with US 82; then from another point on US 82, southwestward via Randolph and Trenton to its junction with US 75; then concurrent with US 75 southward via McKinney to its junction with SH 121 west of Fairview; then southwestward via The Colony, Lewisville, Grapevine, and Bedford; then southwestward via Coppell to Ft. Worth, then southwestward and southward to US 67 in the city of Cleburne, a distance of approximately 100 miles. (Fannin, Collin, Denton, Dallas, Tarrant, and Johnson Counties) At District's request, SH 121 extended along a new location to US 67 in Cleburne.
Does 121 end in Cleburne? I can't find it on any maps. Did it replace TX 174?
It's an under-construction toll road.
South of Ft Worth?
Yes. http://www.dot.state.tx.us/project_information/projects/fort_worth/southwest_parkway/default.htm
I did not know that.
I did not know but I suspected that you did not know that.
Work on the new toll road (Southwest Parkway / Chisholm Trail) commenced in early 2010. Completion is touted for mid-2014.
https://www.aaroads.com/forum/index.php?topic=1270.msg127228#msg127228
TX 121 between McKinney and Grapevine is actually the frontage roads of the Sam Rayburn Tollway, which is not numbered. South of where the tollway ends in Grapevine, the numbered highway rejoins the main lanes and continues (with multiplexes) to Fort Worth.