A door that blocks rails. If you open it, a rail is pushed in from the side, allowing the Minecart to pass through the door without derailing.
With the screenshots, the gate should be easy to recreate. There are 3 outputs in total. One for the lower piston (a), one for the lower piston on the side (b) and one for the upper piston (c). Piston a and c have the same delay (3 ticks). Piston b must be inverted and the signal must arrive here faster and end later, which is why it is connected by a repeater with 1 tick and one with 4 ticks.
If the gate is to be opened with a detector rail, the signal must be inverted.