What is the test for determining whether a public entity is liable for a motor vehicle accident?

Government Code, section 815.6 provides: "Where a public entity is under a mandatory duty imposed by an enactment that is designed to protect against the risk of a particular kind of injury, the public entity is liable for an injury of that kind proximately caused by its failure to discharge the duty unless the public entity establishes that it exercised reasonable diligence to discharge the duty." Thus, imposition of liability here requires a determination that section 44346, subdivision (a)(2) sets forth a mandatory, not discretionary, duty; it was intended to protect against the kind of injury plaintiffs suffered; and breach of the mandatory duty proximately caused the [8 Cal.App.4th 958] injuries. (MacDonald v. State of California (1991) 230 Cal.App.3d 319, 327, 281 Cal.Rptr. 317.) ⁴