Accelerator Rails - Copper

Barring the new Minecart changes and the worry that adjustments to Minecarts will break a lot of existing Redstone contraptions, I think a safer option would be adding a type of Rail that simply makes Minecarts go faster.

Enter Accelerator Rails. Crafted in the same way as Powered Rails, except they use Copper Ingots instead of Gold.

The Accelerator Rail will make minecarts move way faster than a Powered Rail. Input a redstone signal to make them boost any minecarts speed. The stronger the redstone signal, (where 0 is none, and 15 is Super High), the more speed the Accelerator Rail gives, reaching a maximum of 48 b/s (blocks per second) in speed, while a power level of 1 boosts speed to 8 b/s, which is the same as a Powered Rail.

To keep Powered Rails relevant, these are some things the Accelerator Rail can't do:
1. Accelerator Rails only boost minecarts that are already moving fast enough (8b/s or higher), so Powered Rails must be used to send Minecarts off at a high enough speed, or maybe a long slope?
2. Accelerator Rails cannot stop minecarts when unpowered, instead they function as a normal rail.