We probably should have been more forthcoming about this on this particular subforum, but Michigan, and especially the Detroit area, is a sort of de facto test area for the new road type rules
, which are to be the nationwide rules.
The Waze routing server is a complicated thing, but in general Freeways get the highest priority, followed closely by Major Highways; the other types follow behind in descending order. Freeways and Major Highways are the only two types that can be used for any
route — for >200 mi routes, anything between the first and last 100 miles must be one of these two types. How they work in shorter-distance routing is not quite so simple — historical and current speed data are used, but road type still does play some significance, and Freeway and Major Highway are still considered nearly the same. In other words, Waze will not hesitate to use a Major Highway instead of a Freeway where the Freeway is backed up — but Waze still uses
Freeways have always been defined as they are now, as Freeways. Expressways are similar to freeways, but they aren't similar enough to merit the Freeway type — someone who wants to use "avoid freeways" presumably wouldn't mind driving on Metro Pkwy. So they must fall into the next type down, which is Major Highway. But not every alternative to a Freeway is going to be an expressway, so other high-mobility roads need to share the Major Highway type to provide viable alternatives to freeways. A two-lane road can still be a viable option, especially in less-built-up areas. (The other types will also be used to provide alternatives, just not as readily, or as heavily.)
Luckily, MDOT has already answered it for us in their functional classification maps. All the Major Highways you see in Waze are classified as "(Other) Principal Arterials", basically, roads that provide the best facilities for traffic but aren't Freeways. It leaves the guesswork out of road typing.
In short: An expressway is not a freeway, but there is no disadvantage to typing an expressway as Major Highway. Waze will choose between it and other Major Highways (and to a lesser extent other roads) using historical and current traffic speed data.