Three findings:
1. Dwarfs "guiding" a minecart ignore traffic designations on the guidable path. I put a bridge with "high" traffic designation between track paths with "low" and "restricted" (crossroads track all over, to give full guide connectivity). While dwarfs walking through followed the bridge, those guiding a cart just crossed over it, following the geometrically shortest path.
2. "Inside the tick": roller acceleration happens before ramp acceleration; most notably, a cart dragged up a ramp by a roller will cross the ramp at slightly reduced speed (25-28 ticks on a slowest roller) because within the tick, the roller first accelerates the cart to its standard speed, *then* the cart accelerates via ramp and incurs friction, *then* actually moves. A cart emerging from such a ramp will also be checkpoint-compensated back to the roller's operational speed after leaving it. If the roller was taken into account after the ramp, the up-going cart would leave the ramp/roller at roller speed and would be compensated to roller speed + ~5000.
3. There's some strange interaction between insanity and custody: a dwarf with a severe weather allergy was incarcerated for a (fatal) tantrum and went melancholic while tied up. She was not released. She has no pending sentences on the justice tab, the captain of the guard is alive and well and she's "chained" for well over a year now.
That's the other interesting thing (although i've already seen it in .34.11, where it was irrelevant because of the bug that prevented give food/water triggering more than once per imprisonment) - *all* hungry/thirsty caged/chained units will be provided with food and water, including the insane. The mad dwarf's rope is effectively her asylum cell.
I can't find a related bug report (dwarf gone mad while justly imprisoned is not released), this case might warrant one.