In Helfend v. Southern California Rapid Transit District (1970) 2 Cal.3d 1, the Supreme Court upheld application of the collateral source rule and refused to allow the Rapid Transit District, a public entity, to reduce a damages judgment by means of collateral payments to the injured party from an independent source on the grounds that the collateral source rule was not penal in its effect. The court reasoned that the rule expressed a policy of encouraging private investment in insurance for personal injuries and brought plaintiffs closer to full compensation. Because of these compensatory functions, the court held that application of the rule should not be classified as punitive for section 818 purposes. (At p. 16.)