Say "hello" to them.
Once upon a time, one would wave a hand at someone you passed (in respect for sharing the road, neighborly) or, if you were a man, you'd tip your hat at them.
I'd say "hello" in that same respectful way, possibly make a comment about the weather, or the state of the road, nothing overly intimate.
I'd give them a second or two more of my time when I said this, wait for a reply.
If I got one, then we'd be on the way to saying a few things more.
If not, then I'd try it again the next day and the next afterwards...a gradual respectful approach.