Here is the full list of all 18 Tiny Traffic achievements.
Crash 3 or more cars simultaneously
Solve all puzzles in Chapter 4.
Get to the final level.
Finish 100 cars.
Crash two cars into each other, inside a tunnel.
Use a tunnel for the first time.
Crash into a gate.
Crash into a barrier.
Use the reset button 42 times.
Crash 15 cars.
Crash your first car.
Solve all puzzles in Chapter 3.
Unlock Chapter 4.
Solve all puzzles in Chapter 2.
Unlock Chapter 3.
Solve all puzzles in Chapter 1.
Unlock Chapter 2.
Finish your first car.