Arizona Revised Statutes Title 12. Courts and Civil Proceedings § 12-820.03. Affirmative defense; resolution by trial

A. A public entity or a public employee is not liable for an injury arising out of a plan or design for construction or maintenance of or improvement to transportation facilities, including highways, roads, streets, bridges or rights-of-way, if the plan or design is prepared in conformance with generally accepted engineering or design standards in effect at the time of the preparation of the plan or design and the public entity or public employee gives to the public a reasonably adequate warning of any unreasonably dangerous condition.

B. If a genuine issue of material fact exists as to whether the public entity or public employee has met the requirements of subsection A of this section, the issue shall be resolved by a trial before and separate and apart from a trial on damages.