In Phelps v. Firebird Raceway, Inc., 210 Ariz. 403, 111 P.3d 1003 (2005), the supreme court recognized that a written release signed by a professional racecar driver, which exculpated a racetrack owner from liability if the driver was injured in a race, constituted an express contractual assumption of risk. Consequently, the court held that Article 18, Section 5, requires a jury to decide the enforceability of the release even in the face of uncontested material facts. Id. at 405, 410, PP 5, 31, 111 P.3d at 1005, 1010.