What are the elements of a tort action where a plaintiff is injured in a motor vehicle accident?

"The first element, a causal relationship between the plan and the accident, requires proof that the alleged design defect was responsible for the accident, as opposed to some other cause. (Mozzetti v. City of Brisbane (1977) 67 Cal.App.3d 565, 570, 575 [causation was negated by evidence showing poor maintenance and clogging of the drainage system, not merely the system's design, caused the flooding].)" (Grenier, supra, 57 Cal.App.4th at p. 940, italics added.) "If the injury-producing element was not a part of the discretionarily approved design, immunity is defeated." (Id. at p. 941, fn. 7.)