WASHINGTON, DC – The ABI measured 48.5 in December 2013, down from 49.8 in in November. The AIA’s Architecture Billings Index (ABI) stood at 51.6 in October and 54.3 in September. A reading below 50 signifies a decline a monthly “Work-on-the-Boards” survey that is sent to a panel of AIA member-owned firms.