Here is the full list of all 15 Paper Train Traffic achievements.
Accumulate 500 or more stars
Reach the vast cloudy mountains
Reach the quarry and load up on cargo
Reach and load up on goods in the harbour
Accumulate 350 or more stars
Witness the train falling into the depths
Accumulate 250 or more stars
Reach the castle on the high cliffs
Accumulate 150 or more stars
Reach and travel through the forest
Accumulate 100 or more stars
Accumulate 50 or more stars
Complete the tenth level
Accumulate 10 or more stars
Complete the first level