lvin,
when travelling fast, you are exiting the serving cell’s coverage too fast. And during the time the BSC is processing your HO (averaging measurement reports, executing the HO algorithms), the MS may have travelled enough to now be in poor radio conditions.
In worst case, it can take up to 5 seconds before the MS finally receives the HO CMD. (5s is the max. I would say, typically, 2.5s or 3s)
5s @ 130kmh = 180m
that’s enough to get behind a hill, or in a forest… keep in mind the MS was already getting bad coverage, hence the HO detection.
regards
pix