Just as was mentioned about ‘changing lanes’ and ‘accelerating’, you can also learn a lot about someone by ‘how and when’ they decelerate.
Is it timely? How much of it is necessary vs. unnecessary? Are they trying to keep the same gap length or comfort zone? Are they trying to maintain a single speed… or ‘the speed limit’? Are they consciously trying to minimize slowing for themselves and/or for others?
Answering these questions gives you information above skills, abilities and beliefs, which you can then use to your benefit in the moment and in the future.