Powered Rail

The Powered Rail is a block added in Beta 1.5. 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 reset the momentum of any cart to pass over it to a reasonably high speed.

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

Boosting Principle
Powered rails act like redstone wire, and will pass the power to the next adjacent powered rail for 9 blocks from the source. Powered rails have 2 possible states (similar to redstone wire):
 * Off: Stops any minecart that passes over it.
 * On: Boosts any minecart that passes over it, subject to the rules below.

Powered rails (in the "On" state) will boost a minecart if any of the following is true:
 * 1) The minecart is already moving. The cart gets boosted in the direction the cart is traveling, making it possible for 2-way travel.
 * 2) The minecart is stationary, but one end of the powered rail is blocked by a block. The cart gets boosted in the only possible direction of travel (the direction that is not blocked). Used at the start of a minecart trip (launchpad), where the player can push a button to activate the powered rails to start the minecart moving from rest.
 * 3) The minecart is stationary, neither end is blocked, but the powered rail is on a slope. Gravity causes the cart to start moving downwards, which activates (1). Also used in the same manner as (2), but uses gravity to determine the direction boosted rather than a stop block.

A powered rail boost gives an occupied cart enough momentum to travel 64 tiles on a flat surface from a standstill, or an unoccupied cart 8 tiles. Having more than one powered rail next to each other increases the cart's momentum further, however you won't get much additional boost. It appears to respect the 8m/s travel speed limit that traditional cart boosters don't, so a slower minecart gets a larger speed boost and vice versa, thus it is usually unoptimal to place powered rails next to each other, and instead better to space them out at regular intervals. Unfortunately double cart boosters are more practical in the long run, requiring less rare materials and lose virtually no momentum.

The optimal spacing of powered rails is to use 1 every 26 blocks (that is, 1 powered rail followed by 25 normal rails, repeated) which maintains a constant minecart speed of 8m/s. Using 1 every 30 distance results in a negligible 2.6% speed decrease (an increase in travel time by factor of ~0.027 or a speed of 7.8 m/s) if you wish to save on gold ingots. Using 1 powered rail every 32 blocks results in a 10% drop in speed (an increase in travel time by a factor of 1/9 or a speed of 7.2m/s). The player will need to decide on time taken to travel versus amount of resources used when deciding on the powered rails repeating interval (how far apart a single powered rail should be placed every n rails).

4 Powered Rails in a row is sufficient to boost a minecart from rest to the maximum travel speed of 8m/s, so a simple minecart launchpad is to attach a button to the start of the 4 consecutive Powered Rails with a stop block behind it.

Empty Minecarts, an incline and a boost: An empty minecart will move different distances depending on the height of an incline and the location the boost was placed. Using 1 boost, place it on the flat surface at the bottom of the incline. For 2, place one at the bottom (same as using 1) and at the top of the incline (on the angle). Using 2 compared to one will only give around 2m more of a boost. Putting tracks all down the incline and one at the bottom will increase the distance by about 60% of just having one at the bottom. The higher the incline, the farther you will travel. More info in minecarts

Detector Rail
Detector rails power the 4 blocks adjacent to it when a minecart is over it (both occupied and unoccupied). A detector rail next to a powered rail will power the rail while going over it, so that way you can have them powered without it taking up any additional space. If you put the detector rail on one side of the powered rails it will mean that the powered rail will boost you if coming from one direction, but stop you if you're coming from the other, which is convenient to prevent runaway carts from going too far, or on a multiplayer server to make sure people use the rail in the right direction.

If you want the rail to be a 2-way rail, you can put a detector rail on both sides of the powered rail, or simply place a redstone torch or an activated lever adjacent to the powered rail to keep it "on" constantly. 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 travels speed at the top as at the bottom.

Powered Rail Additional Properties
There are currently no curves for powered rails, however, regular rails still prefers 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.

A cart placed next to a solid object (stone, dirt, sand etc.) on a power rail without power, will start moving when the power is turned on. This makes it possible to easily remote start mine carts, or even to build mine cart junctions.

How far the charge passes down adjacent rails is independant 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 normaly despite they should be out of range for the torch.

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)
 * When playing Minecraft in the browser, power rails and detector rails show up as gray blocks but still work.

Trivia

 * Powered rails will always show as powered in the inventory even if destroyed and collected while it was unpowered.
 * Powered rails can curve, but they'll always be displayed as straight pieces.