There is no way to predict the behavior of a strange dog. Period.

IMO, the best thing to do is report these dogs to your local animal control officer. Leash laws have been enacted all over for good reason. You are not a bad person or heartless for doing so; you are protecting yourself, other humans (children, elderly, disabled...) who may not be able to handle the situation, and the dogs themselves from being hit by cars, shot, poisoned, trapped, etc.

I've done it myself on several occasions. If my dog got away, I would THANK someone for caring enough to protect my dog by having him picked up rather than risking all the hazards that could befall the little numbskull.
.


Doc