Frequencies for tow_veh variable in vehnit dataset :

      TOWED |
   TRAILING |
       UNIT |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      1,252       89.88       89.88
          1 |        130        9.33       99.21
          3 |          1        0.07       99.28
          9 |         10        0.72      100.00
------------+-----------------------------------
      Total |      1,393      100.00

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