The hobo fraternity even had the odds against being caught figured out mathmatically. It went like this: 

     500 = The mileage of a train's run 
      x 2 = The number of tracks on the line 
   1000 
    x 15 = the number of daily trains 
15,000 
   : 200 = track mileage patrolled by each 
               R.R. dectective

In practice, however, the theory didn't always work. For example, in one month (October 1921) 20,643 hoboes were ejected from Southern Pacific trains alone. 
"Weary Willies" didn't have an easy time with the railroad "bulls". They were often tossed off moving trains, beaten up, and sometimes, even shot at! 

To avoid detection it was a common practice for hoboes to use a very dangerous method called "riding the rods". They would conceal themselves by using the brake rods beneath the cars. Riding in empty boxcars was more comfortable, but they chances of getting caught was much greater.