Below is a list of the busiest days of each year for Washington's Metrorail system - as best as can be determined. The one highlighted in purple is an imperfect estimate from an online tool.

Year  Event                                                       Day                Ridership

2020 Hockey (18,573)                                    Wen Mar 4 - 675,000 (suspected)

2019 CBF, Wiz (16,616), Baseball(23,050)    Wen, Apr 3 - 756,500

2018 Stanley Cup Celebration         Tue, Jun 12 - 840,145

2017 Women's March on Washington         Sat, Jan 21 - 1,001,613

2016 Cherry Blossom Festival (CBF)             Thu, Mar 24 - 767,000

2015 Baseball (41,291)                 Wen, July 22 - 782,707 

2014 CBF, Baseball (20,869), Miley Cyrus Thu, Apr 10 - 818,076 

2013 CBF, BB(24896), Wizs (20308), Immigration rally         Wen, Apr 10 - 871,164

2012 CBF, Hockey (18,506)         Fri, March 23 - 845,669

2011 Baseball (27,130), US Open Golf         Wen, June 15 - 851,742

2010 CBF, Wizards (18,002)                         Fri, Apr 2  - 891,240

2009 Obama Inauguration Day         Tue, Jan 20 - 1,120,000(est)

2008 Baseball (33,653), WofF conference  Fri, Jul 11 - 854,638

2007 CBF/Baseball (20,894)                         Tue, Apr 3 - 831,508

2006 Immigrant Rights Rally         Mon, Apr 10 - 821,283

2005 Baseball (36,840)                 Thu, July 21 - 769,553

2004 Reagan State Funeral         Wen, June 9 - 850,636

2003 AofGod & Soccer (Barcelona v. Milan) Wen, July 30 - 745,627 

2002 National Rally in Solidarity With Israel Mon, April 15 - 718,747

2001 No Event                 Thu, July 12 - 699,990 

2000 Million Family March         Mon, Oct 16 - 688,467 (*)

1999 CBF                                 Thu, April 8 - 637,305

1998 The highest known day was 7/4 with 585,354, but also know it was lower than 603,766

1997 Promise Keepers                 Sat, Oct 4 - 725,909

1996 Highest known day: 7/4 with 569,894, but know it was lower than 688,467 if a weekday or 725,909 if not

1995 Million Man March                 Mon, Oct 16 - 804,146 

1994 Elton John & Billy Joel concert at RFK Wed, July 20   - 603,706

1993 Clinton Inaugural 1                 Wen, Jan 20 - 811,257 

1992 Only know it was between 529,000 and 565,000

1991 Desert Storm Parade         Sat, June 8 - 786,358 Counted by hand

1990 New Kids on the Block concert Tue, July 17 - 577,800 

1989 George H.W. Bush Inauguration         Fri, Jan 20 - 604,089 

1988 Washington for Jesus rally         Fri, Apr. 29 - 565,000 (but?)

1987 No Event                 Thu, June 25 - 515,047 

1986 Highest known day: 7/4 with ~500,000 but know it was lower than 565,000

1985 Highest known day: 7/4 with ~550,000 but know it was lower than 565,000

1984 4th of July/ Beach Boys Concert         Wed, July 4 - ~ 470,000

1983 20th Anniversary of MLK March           Sat, Aug 27 -  ~370,000 (suspected)

1982 Only know it was between 303,074 and 400,000

1981 Solidarity Day         Sat, Sept 9 - ~400,000

1980 Rally for Jesus         Tue, April 29 - ~400,000 

1979 Energy Crisis                             Tue, June 19 - 306,059 

1978 Highest known day: 9/28 with 212,524 but ridership was up to 222000 by end of year

1977 Highest known day: 10/4 with 141,319 

1976 Opening Day                 Sat, Mar 27 -  51,260