Is this three vertical lines or is it one line?
That will depend on the resolution of your accumulator.

Determining the length of your line: if the input to the hough
transform is a binary image, then the length of any possible line
could be considered to be the value in the corresponding accumulator
bin. However, I would not recommend using this as the length. I
think that the HT is good for getting general positions of lines, but
if you want length/position of lines you need to then use other
methods as well.