I had the minecart max speed at 1000, not sure if that affected it, but I launched myself with a long runup, which shot me about 100 blocks into the air (intended behavior i assume), then i had a spot of unpowered rails at about y=30, and when i landed on these rails, i was slow, but I bounced slowly back where i came from while slowly speeding up instead of coming to a full stop.

https://youtu.be/yaOSOqc6oSw