How are Metrorail Fares Calculated?
Off-Peak Fare Caps
Note that this article speaks of a 27% fare cap:
“To lessen the impact of a large off-peak fare increase for some riders, the percent increase between 2010 and 2012 off-peak fares was capped at 27%.”
When the fares were updated in 2014, the 27% cap became a 47% cap between 2010 and 2014 off-peak fares.