State Highway 40, SH 40, or William D. Fitch Parkway, runs from FM 2154 (Wellborn Road) to SH 6 in College Station. The current SH 40 was authorized in 1994. Signage for the highway went up March 2006 and the road was officially opened June 23, 2006.

SH 40 occupies the overpass and intersection with SH 6 that was formerly Greens Prairie Road, which was truncated and connected to SH 40 by Arrington Road West of SH 6. Greens Prairie Road and SH 40 were renamed in honor of William D. Fitch in August 2006. At SH 6, SH 40 terminates and becomes a local road (maintaining the Fitch Parkway name) continuing northeast to SH 30.

SH 40 begins at an intersection with FM 2154 in College Station, Brazos County, heading southeast on William D. Fitch Parkway, a four-lane undivided road. The road heads near residential subdivisons, becoming a divided highway with the median widening to include woodland. The highway heads through more wooded areas with some fields and residential neighborhoods, turning to the east. SH 40 turns to the northeast and the median narrows, with the road becoming undivided again as it comes to its eastern terminus at an interchange with SH 6.

A previous highway, also called SH 40, existed from before 1920 until the mid 1930s, and ran from the Texas-Oklahoma boundary north of Gainesville down through Denton, Dallas and Beaumont before ending in Port Arthur. There was also a spur route that went from Denton and ended in Fort Worth. All parts of this route were supplanted by highways in the U.S. Highway system by 1935.

The Gainesville to Dallas portion became US 77 in 1929. In 1932, the Dallas to Jacksonville stretch had become part of US 175, while the Denton to Fort Worth spur had become part of US 377. The last remaining portion of old SH 40, Jacksonville to Port Arthur, became part of US 69 in 1935.

Interstates 35E and 35W roughly follow the old SH 40 routes from Dallas and Fort Worth, respectively, to Denton, and the old route from Denton north is approximated by I-35.

The entire route is in College Station, Brazos County.