Level Crossing - with sub routines

As the system becomes more complex, the flow diagrams that are created become more difficult to manage. At this point, sub routines are used.

Create the system below, which carries out the same function as the one you have just created, but uses sub routines.

Create Sub 1 and Sub 2 first - how?
The boxes in the middle part of the flow diagram are normal process commands - help.

Print off your working version, and write on it to explain how it works.