An area to be avoided or ATBA is a ships’ routing measure that comprises an area within defined limits in which either navigation is particularly hazardous or it is exceptionally important to avoid casualties and should be avoided by all ships or certain classes of ships. General Provisions on Ships’ Routing (GPSR) para 2.1.13. In general, these areas should be established only in places where inadequate survey or insufficient provision of aids to navigation may lead to danger of stranding, or where local knowledge is considered essential for safe passage, or where there is the possibility that unacceptable damage to the environment could result from a casualty, or where there might be hazard to a vital aid to navigation. GPSR para 5.5. The IMO instruments providing for the establishment of ATBAs are the Safety of Life at Sea Convention, Chapter V, regulation 10 and the General Provisions on Ships’ Routing.

Additional reference information: 

• National System MPA Definitions and Criteria
• Marine Protected Areas of the United States