Both average daily and annual ridership are included , because only average daily ridership or annual ridership ( not both ) is available for some operators . In cases where data for only one of the two is available , care has been taken to not extrapolate the passenger volume to obtain the other , as there is a potential margin of error when attempting to derive average daily ridership from annual ridership ( which is usually rounded to the nearest thousand passengers ) and natural disasters or other unforeseen situations may force some operators to shut down for extended periods of time , as happened with the Sendai Subway in the days following the 2011 Tōhoku earthquake and tsunami
2011 Tōhoku earthquake and tsunami
2011 Tōhoku earthquake and tsunami
List of urban rail systems in Japan