People v. Superior Court, (1972) 7 Cal.3d 186 at 200
Quoting Taxing Matters
"The second preliminary matter we must consider is the precise point in time at which a traffic violator is "arrested." (4) A police officer may legally stop a motorist to conduct a brief investigation when he entertains a rational suspicion, based on specific facts, that a violation of the Vehicle Code or other law may have taken place (see People v. Griffith (1971) supra, 19 Cal. App.3d 948, 950-951, and cases cited), and the temporary restraint of the suspect's movements incident to that investigation will not ordinarily be deemed an arrest. But when the officer determines there is probable cause to believe that an offense has been committed and begins the process of citing the violator to appear in court (Veh. Code, §§ 40500-40504), an "arrest" takes place at least in the technical sense: "The detention which results [during the citation process] is ordinarily brief, and the conditions of restraint are minimal. Nevertheless the violator is, during the period immediately preceding his execution of the promise to appear, under arrest. [Citations.] Some courts have been reluctant to use the term `arrest' to describe the status of the traffic violator on the public street waiting for the officer to write out the citation [citations]. The Vehicle Code, however, refers to the person awaiting citation as `the arrested person.' Viewing the situation functionally, the violator is being detained against his will by a police officer, for the purpose of obtaining his appearance in connection with a forthcoming prosecution. The violator is not free to depart until he has satisfactorily identified himself and has signed the written promise to appear." (Fns. omitted.) (People v. Hubbard (1970) 9 Cal.App.3d 827, 833 [88 Cal.Rptr.411].)"