Penal Code Section 837. A private person may arrest another:
- For a public offense committed or attempted in his presence.
- When the person arrested has committed a felony, although not in his presence.
- When a felony has been in fact committed, and he has reasonable cause for believing the person arrested to have committed it.
The only possible application of this to a violation of the California Vehicle Code (CVC) is par. 1, which in turn depends on the definition of a "public offense." This is covered in Sections 15 & 16:
PC 15. A crime or public offense is an act committed or omitted in violation of a law forbidding or commanding it, and to which is
annexed, upon conviction, either of the following punishments:
- Death;
- Imprisonment;
- Fine;
- Removal from office; or,
- Disqualification to hold and enjoy any office of honor, trust, or profit in this State.
PC 16. Crimes and public offenses include:
- Felonies;
- Misdemeanors; and
- Infractions.
Felonies and misdeameanors are serious crimes which may be punished by imprisonment, whereas an infraction can only be punished by a fine not exceeding $250 (see below). The applicability of a citizen's arrest to a violation of the CVC thus turns on whether such a violation is an infraction. This is covered below:
PC 17 (d) A violation of any code section listed in Section 19.8 is an infraction subject to the procedures described in Sections 19.6
and 19.7 when:
(1) The prosecutor files a complaint charging the offense as an infraction unless the defendant, at the time he or she is arraigned, after being informed of his or her rights, elects to have the case proceed as a misdemeanor, or;
(2) The court, with the consent of the defendant, determines that the offense is an infraction in which event the case shall proceed as
if the defendant had been arraigned on an infraction complaint.
Finally, the violations of the CVC that can be charged as an infraction are specified in Section 19.8 as follows:
The following offenses are subject to subdivision (d) of Section 17: Sections 193.8, 330, 415, 485, 490.7, 555, 652, and 853.7 of this code; subdivision

of Section 602 of this code; subdivision (b) of Section 25658 and Sections 21672, 25658.5, 25661, and 25662 of
the Business and Professions Code; Section 27204 of the Government Code; subdivision (c) of Section 23109 and Sections 12500, 14601.1, 27150.1, 40508, and 42005 of the Vehicle Code, and any other offense which the Legislature makes subject to subdivision (d) of Section 17. Except where a lesser maximum fine is expressly provided for a violation of any of those sections, any violation which is an infraction is punishable by a fine not exceeding two hundred fifty dollars ($250).
Therefore, the sections of the CVC that can be charged as an infraction are:
Section 23109 (c) - speed contest or speed exhibition on a highway
Sections 12500 - driving on a highway without a valid license
Section 14601.1 - driving with suspended or revoked license
Section 27150.1 - applies to a business installing improper mufflers
Section 40508 - willful violation of promise to appear (re traffic matter)
Section 42005 - failure to attend traffic school
Anyone interested in researching these (and any other) California statutes on your own, can use the following web link:
http://www.leginfo.ca.gov/calaw.html
CONCLUSION: NONE OF THE COMMON CVC VIOLATIONS (SPEEDING, FAILURE TO STOP, GOING THROUGH A LIGHT, CROSSING A DOUBLE LINE, ETC.) ARE PUNISHABLE AS INFRACTIONS, AND THEREFORE A PRIVATE CITIZEN (INCLUDING A SECURITY GUARD) CANNOT MAKE A "CITIZEN'S ARREST" FOR AN ORDINARY TRAFFIC VIOLATION.