clues
first:
use an array of structs to store the position in the spline and desired speed like this:
then do a function that gives you the desired speed based on your spline position from 0 to 1 using the get spline length your are using and so some math.
you can use this too:
make a function that you give the position in the spline and it gives you back the speed target
then use Finterp TO to accelerate from current speed to desired speed:
interp speed = acceleration. higher = faster.
you have all you need:
the length of the spline. you know 0 is the start point and 1 is the end point and how long is it.
delta seconds (time)
and target speed.