If someone changes lanes into a large gap, does the person following slow down to get the same gap back? If so, that tells you what their comfort zone is. Or, do they use the gap to efficiently absorb some of the slowing. Or, do they change lanes timely without causing slowing for anyone. What they do and how they do it will indicate their handling and timing skills.
Important note: Again, ‘reading’ and taking their surroundings into consideration is necessary in order to read their gap and actions properly.