A rail that can set a minecart to a specific speed using redstone signals

I love that Mojang is finally coming around to making minecarts faster, but the problem is that if a global minecart speed is changed, it could mess up some redstone stuff. So I propose having a rail, made out of valuable items (but not impossible to make), that the player can set a speed by using redstone power levels. This way, it only affects the minecart riding over the rail, and it would work by also affecting all powered rails connected to it (and powered rails connected to powered rails connect to it) so it will keep the speed set. For example, if you had 3 redstone blocks next to the rail, it'll set the minecart to 45 b/s (blocks per second) because 15+15+15 = 45. So a max would be 60 (technically 90), and you can use redstone to get anywhere in between. This makes it to where it is up to the player to decide what the speed should be in no-cheats survival, instead of having to use a command to change it, or have to deal with a set speed. The default global speed will still be set to 8 b/s. This could be a good solution to minecart speed improvements, as it still enables creativity, as to get a max speed, players will have to come up with a way to achieve that.