One of the most powerful ways to defeat a design immunity defense in a traffic control device case is to establish that what was actually constructed does not match what was actually approved. Design immunity protects only the specific design that received discretionary approval, not any subsequent modification, deviation, or construction error that produced a different final condition. If discovery reveals that the crosswalk markings, signal timing, or intersection geometry that existed at the time of injury diverged from the officially approved plans, whether through an unapproved field modification, a construction error, or simply the existence of a different, uncertified set of plans that was actually followed, the immunity defense can collapse entirely, regardless of how reasonable the original approved design may have looked on paper. This exact issue arose in litigation involving a young child struck in a marked crosswalk, where investigation revealed a second, unsigned set of crosswalk plans that matched the as-built condition of the intersection, differing from the officially approved design the city relied on for its immunity defense.