What is the relation back doctrine in motor vehicle accident law?

"We later traced the evolution of the relation back doctrine in Smeltzley v. Nicholson Mfg. Co. (1977) 18 Cal.3d 932 [136 Cal.Rptr. 269, 559 P.2d 624, 85 A.L.R.3d 121], and formulated a general rule: An amended complaint relates back to the original complaint, and thus avoids the statute of limitations as a bar against named parties substituted for fictitious defendants, if it: (1) rests on the same general set of facts as the original complaint; and (2) refers to the same accident and same injuries as the original complaint. (Id., at pp. 936-937 [136 Cal.Rptr. 269, 559 P.2d 624].)" (39 Cal.3d at pp. 150-151, 216 Cal.Rptr. 405, 702 P.2d 563.)