Ctrl+F on
minecart wiki1. Ctrl+F "colli" - 2nd is
Danger section - "If an unlucky dwarf or creature fails to dodge a minecart, they can be injured." & "Danger does not always involve living victims: careless route designation can also result in minecarts careening off tracks or colliding with each other. If this occurs, the items may be scattered; this can cause even more hauling jobs than the minecart aimed to eliminate. "
I suppose it could use a clarification that non-minecart items laying on the floor do not affect the minecart - but you presumably observed that yourself.
2. Ctrl+F "speed" - first on page is link to
controlling speed - "Minecarts can reach extremely high speeds, especially when descending multiple Z-levels. A minecart will derail at a track corner if its speed exceeds 0.5 t/st (tiles per step), unless the route in the direction of travel is blocked: "
or Ctrl+F "derailing" - fourth is " "Derailing" can happen when a cart moves at speeds in excess of 50000 - carts will ignore track corners unless forced to obey them by walls or other obstacles blocking the straight path. "
Your case, however, is neither of those - no, it's what's described just below the last - "The "shotgun" effect takes place when a collision changes a cart's movement speed by more than 55000".
What's happening to cause the collision is
cart jumps - " Carts that approach a downward slope at a high enough velocity will also make a jump, (or rather, ignore the ramp and fly forwards) but will not do so if the Checkpoint Effect is exploited through an impulse ramp before the actual downhill as the impulse ramp "tricks" the cart into thinking it has already started going downhill."
Every tile can be a ramp instead - you use twice as many tiles as you need to+whatever you use for slowing down at the end. Bonus note: I generally recommend using bidirectional rampways such as in the moonhome and deathgame maps in my signature, but it's too much of a hassle to readapt; I'd instead ensure minecart always enters the descending rampway at same speed and build track stops as necessary to stop the jumping into a wall. (you can later link the stops to levers to ensure the cart does jump at desired z-level, and, say, through a fortification).