Describe the bug
Trains gain velocity when going down on a long slope and up on a short one.
How to reproduce
Steps to reproduce the unwanted behavior:

1. Go build this:
   
2. Drive a train down the long slope so it is able to climb the short one at least once and then turn off the engine
3. Watch the speed increase every loop

Expected behavior
For me (modified slope climbing value) the train gains a few km/h every loop.

Screenshots
If applicable, add screenshots to help explain your problem.

Can't reproduce on "reasonable" slopes, closing.