Missouri Secondary State Route AB is a short east-west highway in Central Boone County. It runs from U.S. Rt. 63, east to the Mark Twain National Forest. MO Sec St Rt AB does not pass through any towns in Boone County. MO Sec St Rt AB is not multi-plexed in Boone County. MO Sec St Rt AB intersects the following highway in Boone County. U.S. Rt. 63, near Columbia.