Apple recently updated its Maps app to add transit directions and data for Tucson, Arizona. Transit directions have been available in Phoenix, Arizona since October of 2017, but transit information for Tucson appears to be new.
Apple Maps users in Tucson can now select public transportation routes when getting directions between two locations, with SunTran bus lines available as a transit transportation option. Amtrak routes are also available, and have been for some time.
Apple has not yet added Tucson to the website where it lists locations where transit directions are available, but it should be added in the near future.
Transit directions were first added to Apple Maps in 2015 with the launch of iOS 9. Maps initially only offered transit information in a handful of cities, but over the course of the last three years, Apple has worked to expand the feature to additional areas.
Transit information is now live in dozens of cities and countries around the world, with a full list available on Apple's iOS 11 Feature Availability website.