With the Maps app in El Capitan you can now search for transit directions. If this is available in your city, you'll be able to see how to get from one point to another using public transportation. You can specify the start time or arrival time and often can choose between many options. You can share these directions with your mobile device or print them. You can also simply view transit lines without setting start and end points.
I am definitely looking forward to having Transit directions for Seattle!