The Mass Transit Add-on for Cities: Skylines has 10 achievements.
Have 10 monorail lines
Have 3 monorail lines
Have 3 ferry lines
Have 15 ferry lines
Transport 5 000 passengers with Cable Cars
Transport 20 000 passengers with Cable Cars
Have 3 blimp lines
Have 10 blimp lines
Have one Ferry and Bus Exchange Stop, Metro-Monorail-Train Hub, Monorail-Bus Hub and Multiplatform Train Station
Win all three Mass Transit scenarios