Mahaffey v. State, 2012 Tex. Crim. App. LEXIS 631

Mahaffey charged with DWI after being stopped for failing to signal a lane merge on Highway 198 near a lane-end sign.
Officer testified the right lane ended and Mahaffey merged left without signaling.
Trial court denied suppression, concluding the stop was based on a 545.104(a) signal violation.
First appellate court held signaling required for a merge between lanes, leading to Mahaffey I reversal remand.
On remand, the court of appeals again found the statute broad enough to require signaling for the merge.
Texas Crim App reverses, holding the merge where lanes end is not a lane change requiring a signal under 545.104(a).
The Court concludes there was no reasonable suspicion to justify the stop, so suppression should have been granted.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Does a lane-ends merge constitute a lane change requiring a signal?	Mahaffey: merge ends while two lanes become one; no lane change.	State: any lateral movement to a different lane is a lane change; signal required.	Yes, it is not a lane change; no signal required.
Was the stop supported by reasonable suspicion under 545.104(a)?	Mahaffey: no legal basis for signal requirement; stop improper.	State: officer reasonably believed a violation occurred.	No reasonable suspicion; suppression required.

Mahaffey v. State, 316 S.W.3d 633 (Tex. Crim. App. 2010) (held merge not a 'turn' and signaled condition limited to certain merges; clarified literal statute interpretation)
Turner v. State, 261 S.W.3d 129 (Tex. App.-San Antonio 2008) (distinguishes lane-change signal requirement at intersections and designated lanes)
Trahan v. State, 16 S.W.3d 146 (Tex. App.-Beaumont 2000) (merger/exit signaling—cite not mandatory authority; supports narrow ruling)
Hernandez v. State, 983 S.W.2d 867 (Tex. App.-Austin 1998) (laned roadway; drift across markings not always a lane change)
Fowler v. State, 266 S.W.3d 498 (Tex. App.-Fort Worth 2008) (limits scope of when lane-change signaling is required)