Unit Deacceleration

[PicassoCT]

If a unit approaches its target destiny, and starts to deaccelerate, is there a sort of flag that is set or any other way to get that info, besides comparing speeds all the time, and filtering it out if some sudden downward curve appears?
I dream of something not ressourceexessive, not demanding that i call spring all the time, buggering it for the units xz coordinates so i can get the distance out of its vector.