Powered Rail

The Power rail is a block added in Version 1.5. They replace bug boosting (boosters will still work after the update). It was tweeted by Jeb first to prepare texture pack makers where it will be. It will have 2 states, powered and unpowered. The Powered Rail was implemented in the Beta 1.5 on April 19th, 2011.

Boosting Principle
When a minecart passes a powered powerrail, it will be boosted. This will only work when you have a certain speed, powerrails will not launch your cart. If a powerrail is unpowered, it will stop the minecart. Powerrails act like redstone wire, and will pass the power to the next adjacent rail for 9 blocks from the source.

If a Powered rail is not connected to a active redstone dust, it will not act like a boost, but like a brake, and stop the Minecart quickly.

A single powered rail will not provide much speed increase, but multiple powered rails together will boost the speed further.

Powered Rail Additional Properties
There are currently no curves for powered rails.

A cart traveling on a powered rail that collides with an object (wall, single block, player, other cart) will reverse direction. 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 eachother on a short track designed this way can be used to chain multiple carts together as a "train". Once alligned, they will all move together at relatively the same speed.