Ability to slow down Minecarts

After playing around with the experimental minecart changes, I've found that there is one feature that is lacking: the ability to easily slow a minecart down. I've tried unpowered powered rails, but they appear to instantly stop even the fastest-moving minecart. Soul sand doesn't appear to do anything, either. All that I have found to slow carts down is a vertical climb on regular (or equivalent) rails. However, it takes 34 blocks of vertical climbing to erase all momentum of a cart at a fairly-reasonable 32 blocks per second pre-climb. Practically speaking, this means any minecart system that requires any redstone or player interaction, which is unreliable at high speeds, needs to refrain from ever reaching such speeds unless there is room for quite a long uphill climb. I'm requesting that there be some way to slow carts down without needing a large hill, and without stopping them completely. Whether through a new rail type, changing unpowered rail behavior, or something else altogether, I leave to the developers.