Ok, I know this isn't a bug, but I think it should be re-implemented. The problem is that the faster minecart speed was removed. I found it simple just to place a single unpowered rail before bends or uphill sections. I have a cool track that doesn't work now because the leaps off tracks aren't very big 😞
Please re-implement it Mojang. It was good. I (and a few others) didn't mind. My track even used the derailing thing at one point (I don't mind if that gets fixed). Please.