Why are there no transit directions on my iPhone 4s?

Transit directions for select cities (Baltimore, Chicago, New York, Philadelphia, San Francisco, and Washington in the U.S.) were added to Maps in iOS 9, but the feature is only supported by the iPhone 5 or later, both iPad Air models, the iPad mini 2 or later and the sixth-generation iPod touch. This means the iPhone 4s, iPad 2 and 3 or fifth-generation iPod touch will not give you a transit option in the Maps app.