why will siri not honor avoid highways?

I've been having the same problem lately. It doesn't happen every time, but it's very annoying. Doesn't anybody have a suggestion?

Your definition of “highways” may be different from Siri’s. And it isn’t Siri that does the routing; that is the Maps app. Do you have “avoid highways” enabled in the Maps app? And note that “avoid” won’t be honored if there is no reasonable way to get to the destination without using a highway. In the US, at least, “highway” specifically means a road that is part of the Eisenhower Interstate Highway System.

As an example, I once enabled “Avoid tolls”. I then plotted a route from Fort Lee, New Jersey to Manhattan, a trip that is less than 5 miles, but requires crossing the Hudson River. It created a 7 hour route that avoided tolls by sending me up the West side of the Hudson 140 miles to Troy NY, where there is a free bridge across the Hudson, then back down the East side of the Hudson. Later versions ignored the Avoid Tolls.