In the 11-3 crossover sequence, which action is first?

• A. Movable frog first halfway
• B. The first switch
• C. The middle switch point machine
• D. Finish throwing frog

Answer: (A)

The sequence always starts by setting up the transition state before any switching happens. In this crossover, you begin by moving the movable frog halfway. This initial positioning creates the proper intermediate configuration that allows the rest of the steps to occur safely and in the correct order. Once the movable frog is halfway, the system can then proceed to the first switch, then engage the middle switch point machine, and finally complete the action of throwing the frog. Trying to perform switches or finish the frog without first positioning the movable piece would leave the track in an undefined or unsafe state, which is why the very first action is moving the movable frog halfway.