The rationale for design immunity is to prevent a jury from second-guessing the decision of a public entity regarding a particular plan or design of a public construction or improvement. (Baldwin v. State of California (1972) 6 Cal. 3d 424, 432, fn. 7, 434, 99 Cal. Rptr. 145, 491 P.2d 1121; hereafter, Baldwin.) "To permit reexamination in tort litigation of particular discretionary decisions where reasonable men may differ as to how the discretion should be exercised would create too great a danger of impolitic interference with the freedom of decision-making by those public officials in whom the function of making such decisions has been vested." (Cameron v. State of California (1972) 7 Cal. 3d 318, 326, 102 Cal. Rptr. 305, 497 P.2d 777.) Or to put it another way, "in enacting section 830.6, the Legislature was concerned lest juries be allowed to second-guess the discretionary determinations of public officials by reviewing the identical questions of risk that had previously been considered by the government officers who adopted or approved the plan." (Baldwin, supra, 6 Cal. 3d at p. 434.) Public entity can be liable for injury caused by a dangerous condition of its property. ( Gov. Code, 835.) the state's failure to erect median barriers to prevent cross-median accidents may result in such liability. (Ducey v. Argo Sales Co. (1979) 25 Cal. 3d 707, 720, 159 Cal. Rptr. 835, 602 P.2d 755; Morris v. State of California (1979) 89 Cal. App. 3d 962, 965, 153 Cal. Rptr. 117.) Government Code section 835 provides: "Except as provided by statute, a public entity is liable for injury caused by a dangerous condition of its property if the plaintiff establishes that the property was in a dangerous condition at the time of the injury, that the injury was proximately caused by the dangerous condition, that the dangerous condition created a reasonably foreseeable risk of the kind of injury which was incurred, and either: (a) a negligent or wrongful act or omission of an employee of the public entity within the scope of his employment created the dangerous condition; (b) the public entity had actual or constructive notice of the dangerous condition under Section 835.2 a sufficient time prior to the injury to have taken measures to protect against the dangerous condition." However, statutory law provides a "design immunity" defense to such liability. ( 830.6.) Under section 830.6 there is no liability for an injury caused by the plan or design of a construction of or improvement to public property where such plan or design has been approved in advance of the construction or improvement by the legislative or other authorized body of the public entity provided the trial or appellate court determines that there is any substantial evidence that a reasonable legislative (or other authorized) body or public employee could have adopted or approved the plan or the design or standards therefor. Thus, a public entity raising a design immunity defense must establish three elements: (1) a causal relationship between the plan or design and the accident; (2) discretionary approval of the plan or design prior to construction; (3) the existence of substantial evidence supporting the reasonableness of the adoption of the plan or design. (Higgins v. State of California (1997) 54 Cal. App. 4th 177, 185.) Section 830.6 provides: "Neither a public entity nor a public employee is liable under this chapter for an injury caused by the plan or design of a construction of, or an improvement to, public property where such plan or design has been approved in advance of the construction or improvement by the legislative body of the public entity or by some other body or employee exercising discretionary authority to give such approval or where such plan or design is prepared in conformity with standards previously so approved, if the trial or appellate court determines that there is any substantial evidence upon the basis of which: (a) a reasonable public employee could have adopted the plan or design or the standards therefor or (b) a reasonable legislative body or other body or employee could have approved the plan or design or the standards therefor. Notwithstanding notice that constructed or improved public property may no longer be in conformity with a plan or design or a standard which reasonably could be approved by the legislative body or other body or employee, the immunity provided by this section shall continue for a reasonable period of time sufficient to permit the public entity to obtain funds for and carry out remedial work necessary to allow such public property to be in conformity with a plan or design approved by the legislative body of the public entity or other body or employee, or with a plan or design in conformity with a standard previously approved by such legislative body or other body or employee. In the event that the public entity is unable to remedy such public property because of practical impossibility or lack of sufficient funds, the immunity provided by this section shall remain so long as such public entity shall reasonably attempt to provide adequate warnings of the existence of the condition not conforming to the approved plan or design or to the approved standard. However, where a person fails to heed such warning or occupies public property despite such warning, such failure or occupation shall not in itself constitute an assumption of the risk of the danger indicated by the warning." This is how the section presently reads. Prior to 1979, it did not contain the second and third sentences. As we explain, the Legislature added those two sentences to section 830.6 in 1979 in response to a limiting construction of old section 830.6 by the Supreme Court.