What is the legal test for determining whether a sheriff's negligence was a direct cause of action under the California Highway Traffic Safety Act?

It should be noted that subsection (a) of Government Code, section 1953, imposes a more rigid requirement; the injury must be the direct as well as proximate result of the condition. In construing this section, Hinton v. State of California, 1954, 124 Cal.App.2d 622, 626, 269 P.2d 154, 157, held the use of this word increased the plaintiff's burden. The court defined direct cause therein as "the active, efficient cause that sets in motion a train of events which brings about a result without the intervention of any force started and working actively from a new and independent source,' * * *' In our opinion, the incompetent driving by the escaping prisoners was definitely an intervening cause which prevents the sheriff's negligence, if any, from being a direct cause, and for that additional reason appellants have not met the requirements of stating a cause of action under the act.