In Uyeno v. State of California (1991) 234 Cal. App. 3d 1371, a 10-year-old boy was killed in a pedestrian crosswalk. The plaintiffs alleged that the traffic light sequence should have used a two-second all-red mode instead of a half-second all-red mode, to allow vehicular traffic to clear before pedestrians were allowed to proceed. The plaintiffs argued that the timing of the signals was not a "plan" or "design" subject to the design immunity because the timing was not determined in advance of its implementation. (Uyeno, supra, 234 Cal. App. 3d 1371, 1377.) The court ruled, however, that the operation of the traffic lights, including the timing, was integral to the system. "When a part of an improvement is integral to its function, it must be considered to be within the scope of the design for that improvement, even if it is to be later formulated." (Uyeno, supra, 234 Cal. App. 3d 1371, 1377.) In terms of prior approval, the evidence in Uyeno showed that a timing plan was prepared after the traffic signals were constructed, based upon usage data and prepared guidelines. Inasmuch as signal timing "requires some observance in operation and does not readily lend itself to a full preimplementation determination," (Uyeno, supra, 234 Cal. App. 3d 1371, 1379.) the signal operator's on-site approval and later preparation of a report satisfied the requirement of prior discretionary approval. At least "the light intervals are approved before the public is left to rely upon the signals." (Uyeno, supra, 234 Cal. App. 3d 1371, 1379.)