Seeing as the Roller Coaster contest has just come out, I figured some people might want to add a little... action to their tracks. What's better in a cave than an open pit of lava, suddenly being covered with a track to pass over, then retracting? This simple tutorial is the base requirement for the timing necessary to move a rail AND the block that supports it.

Allow me to stress one point: You CANNOT just put 2 pistons on top of each other like you would a piston door. The rail WILL break if you do.

A brief description of what will occur:
On Retraction:
(+) The track will retract, then the supporting block will retract
On Extension:
(+) The supporting block will extend, then the track will extend

Now that that's out of the way, on to the setup.

You can have any kind of input running into this device. Most likely, the majority of you will be using a detector rail. If you do so, be sure to add the proper amount of an extension to the current you're supplying through the use of a current extender (Figure 6). This will need to be put in BEFORE the split in current to the two moving pieces. The current extension length will be relative to the size of the amount of track you're moving.

Once you have your desired time for activation set, create a split in your current. The first will go to the piston controlling the placement of your supporting block(s) (Figure 2). I've set the current to this section to be 8 ticks long (two repeaters fully delayed) to give myself adequate buffer room, in case a pulse is jumbled or something.

The second section (Figure 3) is where most people would become confused.
Firstly, a direct current must be applied to the Track Extension piston. (Lapis)
Secondly, bridging from the direct current, a delay must be added that is LONGER than the delay in Figure 2. (Emerald)
I've heard that 2 ticks is all that one needs, but I err to definite results, and have made my delay 16 ticks long, which is double the length of the delay in Figure 2.

Now, you may wonder why the second delay in Figure 3 is longer than the delay in Figure 2.
The current provided by the (Emerald) delay is what keeps the track from extending before the supporting block is back in place.

This is really all it is. The currents length can be changed, so long as they remain relative to each other in the scale I've displayed (one always shorter or longer than the other). I'm aware that I may have missed something, or may have made this a bit more confusing than necessary, or even confused you in reading. If so, please ask me questions about the issue you encounter.

I hope you find this little gadget helpful in your roller coasters. I'll be putting up other devices I find to be cool that you guys might like to use. Best of luck in the coaster contest!