Frequencies for rail variable in accident dataset :

 Rail Grade |
    Xing ID |      Freq.     Percent        Cum.
------------+-----------------------------------
    0000000 |        570       99.82       99.82
    9999999 |          1        0.18      100.00
------------+-----------------------------------
      Total |        571      100.00

by Jean Roth , jroth@nber.org , 18 Apr 2016