Game layout generator (no dead ends)

Question

I'm trying to make my very first game using Stencyl. The game is based on a very simple concept but I am finding it difficult to generate the levels.

This is how the game works, the player is stationary and is able to change lanes to the left and right, the actual 'obstacles' (horizontal and vertical lines) moves down. I need to somehow generate these horizontal and vertical lines in a way that the player is never 'trapped' (i.e. all four lanes are NEVER blocked off at any one time).

My initial idea was to create a few different layouts (10-30) and spawn a random layout off screen (top) which then moves down. The problem with this is that it is not very efficient memory wise.

I am thinking of creating some sort of layout generator that will create and spawn possible layouts. I am open to using different software/tools if need be. Any guidance would be appreciated. Example of what I am trying to avoid