Powered Rail

The Powered Rail is a block that is used to power carts. It was added to replace bug boosting, but as of Beta 1.5 boosters still work. It's operated by Redstone currents. In its unpowered state, it acts as brakes for any minecart which crosses its tile. In its powered state it will accelerate any cart to pass over it, up to the maximum speed of 8 m/s, at which point only a small amount of additional momentum can be added with powered rails.

Crafting
Powered Rails are made somewhat differently from normal rails; using gold instead of iron, and adding redstone to the bottom.

Effects
Powered rails, much like redstone wire, have two possible states: on or off.

A rail that is "off" slows any passing minecart by applying a frictional force. The force is generally strong enough to bring a moving minecart to a complete stop, or to hold a minecart in place on a slope.

A rail in the "on" state will accelerate a minecart if any of the following is true:
 * 1) The minecart is already moving, in which case the cart is accelerated in the direction of motion
 * 2) The minecart is stationary, but one end of the powered rail is up against a solid block. In this case, the cart is accelerated in the direction that is not blocked.
 * 3) The minecart is stationary, but the powered rail is on a slope. The instant the powered rail is activated, the brake is released and the cart will start moving down due to gravity. As the cart is now moving, rule (1) applies and the cart is accelerated in that direction.

The second and third cases can both be used to create simple stone button-activated launchpads. When the powered rail is off, carts are held in place, providing a safe way to load and unload carts without them derailing like they would on pressure plates.

Powering
Power can be transmitted to the rail from any of the six adjacent positions (above, below, or any side) in the same ways that redstone wire is powered. Strangely, the rail can also receive power from the five positions immediately above those adjacent positions. In other words, the rail acts as if it is two blocks high, and can receive power through any of eleven adjacent spaces, just like a door. This works whether the upper space is occupied or empty. However, powering the rail through the upper space currently exhibits more bugs related to updating.

Powered rails will propagate power to each other if they are adjacent and part of the same track, for up to 9 blocks from the power source. They will also receive power from any adjacent detector rail, even if they are not part of the same track (which follows from the rules above).

To activate power rails only when necessary, use detector rails:
 * For one-way travel, place a detector rail before the powered rail
 * For two-way travel, place a detector rail on both sides of the powered rail

For the two-way case, it is far more efficient to have powered rails constantly active using other means:
 * Place a Redstone Torch either next to the powered rail or two blocks underneath it or use powered Redstone wiring to achieve the same effect
 * Place an activated Switch next to the powered rail

Optimal use
A powered rail boost gives an occupied cart enough momentum to travel 64 tiles on a flat surface from a standstill, or 8 tiles for an unoccupied cart. Unlike the boosters, powered rails will not provide the cart with much momentum past the cart speed limit of 8 m/s. Thus it is usually impractical and expensive to place powered rails one after the other. Instead, space powered rails out at regular intervals once the cart is initially traveling quickly to maintain speed.

However, to launch carts from rest using only powered rails, four powered rails in a row is sufficient to boost a cart to the maximum travel speed of 8 m/s. It is easy to construct a simple cart launcher by placing a block, a single powered rail, a regular rail, then four powered rails and attach a button near the single power rail. Activate the four rails by other means so that they are always on. The activated button will launch the cart toward the group of four rails and will quickly reach top speed. An example of this is shown in the Effects section, above.

Once at speed, the optimal spacing of powered rails on a level track is to use 1 every 26 blocks (that is, a repeating pattern of one powered rail followed by 25 normal rails, then another powered rail, and so on) which maintains a constant minecart speed of 8 m/s. If gold is in short supply, it is possible to use powered rails with more space between them at a cost of a reduced overall speed: By using 1 powered rail every 26 blocks, you can easily match this with using one standard torch every 13 blocks which keeps the entire track at light level 7 and above since hostile mobs can spawn on tracks (non-hostile mobs will only spawn on tracks if the track is on dirt with green grass).
 * One powered rail every 30 blocks: 7.8 m/s–2.6% speed decrease
 * One powered rail every 32 blocks: 7.2 m/s–10% speed decrease

For diagonal tracks on level ground, the optimal spacing of powered rails (before you need to break the diagonal in order to do a 3x1 straight stretch to use a powered rail) is 1 every 36 blocks (counting orthogonally, if you count diagonally instead it is 1 every 18 blocks). It is worth noting that 36 is roughly equal to 26 multiplied by the square root of 2, which is the actual distance one would travel diagonally (by Euclidean math) if a player moved 26 blocks on both coordinate axes.

Climbing slopes
Launching from rest via four powered rails, an occupied cart has enough momentum to climb a 1/1 slope six blocks high without further boosting and then travel horizontally at a very slow speed for at least a dozen blocks before coming to a stop. Such a cart does not have enough momentum to climb a seven block high slope. Thus, additional powered rails are required to climb higher slopes or exit the climb at a faster-than-walking speed. An unmanned cart in a similar setup will only climb three blocks and then travel a few blocks horizontally.

A worst-case scenario would be placing a powered rail every other block to maintain the 8 m/s speed limit. This means that for every two blocks of height climbed, a gold ingot is required. Rails on a slope must be activated externally via redstone or a lever but not via a detector rail. Carts will not maintain enough speed to clear a powered rail before the detector rail deactivates, returning the powered rail to its braking state.

Use with Detector Rails
A Detector Rail will power the 4 blocks adjacent to it as well as the 2 blocks below it when a minecart (both occupied or empty) is over it. It is thus possible to activate powered rails inline without the use of redstone torches or wiring. This lends itself to one-way powered rail lines by placing a detector rail before the powered rail (with respect to the desired direction of travel). This way, occupied carts will only be boosted if they are traveling the proper direction. Carts coming from the "wrong" way will be quickly brought to a stop by the inactive power rail. A two-way line can be inefficiently created by placing detector rails on either side of the powered rail.

Placing alternate powered and detector rails up a 1/1 slope will not propel a cart of any kind more than 3 blocks upward due to a lack of speed, which is required to clear the booster before it returns to the "off" state. The cart will become stuck unless it is in a "train" of two or more carts, in which case the last cart in the train will become stuck. To go up a slope properly, the whole slope needs to be powered rails powered externally by redstone torches in order to maintain speed the same speed at the top as at the bottom.

Additional properties
Curved power rails currently only exist in the case of a T-junction. They do not currently function like regular rails in a curve (without being in a junction). It is possible to make a one-way curved railway using power rails, but not a bi-directional one.

When placing rails, regular rails prefer to curve towards the powered rail. In cases such as these, the south-west rule applies.

A cart traveling on a powered rail that collides with an object (wall, single block, player, other cart) will reverse direction. It will not reverse direction if it collides with a translucent block, such as Stone Slabs or Glass. If a track including powered rails is bordered by blocks acting as "buffers", the cart will indefinitely continue back and forth along the track. Having carts interact with each other on a short track designed this way can be used to chain multiple carts together as a "train". Once aligned, they will all move together at relatively the same speed.

How far the charge passes down adjacent rails is independent of the length of redstone wire. Even if the rails are connected to a redstone torch by 15 blocks of redstone dust, the rails will still be powered normally despite the fact that they should be out of range for the torch.

Stop Points
It is possible to make points in your track where a cart is stopped and then jumpstarted again by player input. This can be useful for creating checkpoints to certain sites of interest in your world. This can be done by using two powered track pieces on a one block incline, by having the first powered track piece going down, with the second powered track piece at the bottom and a button placed alongside the second powered track piece, so that the button is directly above the track. You can see an example of a stop point here.

When the cart comes to this point it will stop On the incline, allowing the cart to use gravity to start the boost when the button is pushed. Players can then either stay in the cart and carry on to the next stop, or leave the cart at the station for themselves/other players to use later.

Starting boost
Creating a simple initial boost device using 2 powered rails. Dig a hole 1 block deep and 2 blocks long. Place the powered rails inside the trench, connect one end to the track that you wish the mine cart to exit. Finally place the mine cart on the powered rail. Once power is applied to the rail the mine cart will be boosted out.

Bugs

 * If a Powered rail is only powered by another Powered rail diagonally up or down, you can destroy the rail powering it and it will continue to look and act like it has power until the block is updated. This can be used to have little to no power sources in your track design and up to 2/3 less powered tracks for uphill parts.
 * When you power a track, 8 tracks in both directions (excluding the track being powered) will be powered. If you have a 19 Powered tracks in a row [1,2,3...18,19] and you Power track 10, tracks 2-9 and 11-18 will receive power. If you add power to track 9, after powering track 9, track 1 will not be powered, even though it is within the 8 tracks. After this, if you remove power from track 10, power will be taken from track 9, however, the same tracks will be stay powered (tracks 1 which should be powered is not, and track 18 which is powered, should be unlit). If you power track 2, (or 18), you will get power in the next 8 blocks.
 * Doing this, you can power infinite tracks with only 3 torches. 1) If you power track 1, up to track 9 will be lit. 2) Power track track 9 (or last lit track) and 10 (the last unlit track). Putting power in track 9 will keep the previous tracks lit, and 10 will power the next. 3) Then unpower 1, it will still be lit, as 9 is lit, and in the 8 range. 4) Now unpower 9. 1 is still lit. Jump back to step 2.
 * This also means you can't power tracks in steps of 1 (unless you make something fancy with redstone circuitry). You would have to unpower everything, then power the one 8 steps away (you need n carts + 8 for the number of tracks)
 * There are currently no textures for curved power rails. However, they still work when placed at T-junctions powered by Redstone.

Trivia

 * For comparison of speeds, walking speed is about 4 m/s (4.27 exactly), thus using powered rail to speed up will almost double your traveling speed.
 * Powered rails will always show as powered in the inventory even if destroyed and collected while it was unpowered.
 * Noting that it takes 6 Gold Ingots to make 6 Powered Rails, it might be more resourceful to use bug boosters. However, bug boosters might be removed/fixed by Notch in the upcoming Patch 1.6.
 * When a powered rail with power has another powered rail added next to it, the second rail will not light, until the power is reset.