Calibrated rails

Instead of making minecarts faster, add calibrated rails. These types of rails will work like powered rails, but you could adjust the velocity level of these. So if a signal with the power of one comes into the rail, the minecart would go super slow but if a signal with the power of 15 comes into the rail it would go three times the speed a minecart normally goes! The calibrated rail would be crafted with a powered rail in the middle, iron in all corners, an amethyst shard at the top and redstone dust in the rest.