Amends GS 136-44.51(b) as the title indicates. Sets the time limit for the real property to be encumbered by a transportation corridor official map (map) at 18 months from the date of the adoption of the map (was, three years from the date of the original submission of the application for a building permit or subdivision plat approval for real property subject to a valid map). Permits the owner of the real property within the transportation corridor to treat the real property as unencumbered if the entity that adopted the transportation corridor official map has not purchased the property or initiated condemnation proceedings on the property within the 18-month time period. Effective December 1, 2011, and applies to all transportation corridor official maps filed on or after that date.