Frequencies for tow_veh variable in vehicle dataset :

      TOWED |
   TRAILING |
       UNIT |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |        613       97.46       97.46
          9 |         16        2.54      100.00
------------+-----------------------------------
      Total |        629      100.00

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