Year including construction (constant 2010 US$) 1991 20778.7611011786 1992 21430.2415368182 1993 19645.5553304248 1994 18247.2950021867 1995 17004.9823587441 1996 17497.7849499816 1997 17450.6436953218 1998 17336.4751528301 1999 16165.2097411019 2000 16666.9677569611 2001 17415.5243549278 2002 16942.2257732516 2003 18572.01423855 2004 18847.934164829 2005 18760.0124196585 2006 18154.8579548654 2007 17408.4447538448 2008 16583.1855657558 2009 16799.3776227431 2010 16825.3349370516 2011 17618.5275283132 2012 17542.7127438062 2013 17382.8975119657 2014 18223.0995634128 2015 17644.0755518331 2016 15931.8394460058 2017 15810.3887546688 2018 15681.9948384633