Detector Rail

Detector Rails are blocks to be added in 1.5. They are planned to act like pressure plates but will be a type of rail, allowing minecarts to move over them.

When any kind of minecart is on top of the Detector Rail, it will generate a redstone signal. It is not confirmed which blocks receive this redstone signal, but if it acts like a regular pressure plate then the receiving block will be the one underneath the rail, as well as those directly adjacent to it horizontally.

Crafting
Detector rails are crafted as normal rails, but with a pressure plate instead of sticks, and the addition of redstone.

Wood pressure plates don't work!