so giant momentum building minecart glich

Hello i was playing aroun and i've found this (pls go to this link) https://youtu.be/dLx6Kq9Kddo

its a vidieo of the glich 
if u need more info of how i've done it
message me on this post (im new on this site)
also comment on youtube

Edit: if I push the minecarts they start full speed again