To successfully sue the following must be proven:
That the public entity had actual or constructive notice of the dangerous condition in enough time to have corrected it before the accident.
That the measures taken by the public entity, or the failure to take any measures, in response to the dangerous condition were palpably unreasonable.
Also take into account the the judge is provided with the following guidelines:
A public entity like the defendant must constantly exercise its judgment whether to seek or to provide the resources necessary to hire personnel, buy or repair equipment, build or maintain facilities, and, in general, decide where, when and how to provide adequate governmental services. In exercising its judgment and making those choices, a public entity is frequently faced with competing demands, not all of which can be satisfied at once or perhaps at all. A public entity does not have the duty to do everything that might be done.