Belfast·SPG009 Retail and Main Town Centre Uses·Page 20·3.3.4
Design Year for Impact Testing
The design year should represent when the proposal achieves mature trading patterns, conventionally taken as the second full calendar year after opening, though some developments may take longer to establish.
The design year for impact testing should be selected to represent the year when the proposal has achieved a 'mature' trading pattern. This is conventionally taken as the second full calendar year of trading after opening of each phase of a new development, but it may take longer for some developments to become established.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/belfast/SPG009 Retail and Main Town Centre Uses.pdf