In the object animation panel you can select viewport animation. An animation triggers when the user scrolls and the element appears in the current viewport.
Viewport animation
example end of viewport
Scroll down to view elements initially outside your current viewport
SHOW GROUP
Click the button to show the group of cars
A group contains a new timeline, when the group is visible it will start the timing of its own elements.
Extra timeline
Delayed animation
End animation
Repeating animation
Start animation
