Frequencies for tow_veh variable in person dataset :

    VEHICLE |
   TRAILING |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |        647       79.29       79.29
          9 |         29        3.55       82.84
          . |        140       17.16      100.00
------------+-----------------------------------
      Total |        816      100.00

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