The goal is to get the requested number of trains from a "Start" station to a "Goal" station, merging and mixing trains if necessary. Later levels will introduce paint tiles that will change the color of any Train that enters it, and scissor tiles that will divide a train colored with a secondary color into two primary-colored trains (or just duplicate them if they're already primary when entering). There's also the color Brown, which is usually treated as a useless color that sees little to no use in the levels.
A year following the original game's release, a Level Editor was added, where players can create and share level designs, and view/submit custom solutions for them as well.
This game has the following Tropes:
- Colorblind Mode: Present in the game is an option to apply letters to each color.
- Colour-Coded for Your Convenience: The trains themselves; It's a game about colors, after all. In total, there are seven colors: all the primary and secondary colors, plus a brown color if a secondary is mixed with a primary or a non-matching secondary.
- Freemium: The free version of Trainyard, known as Trainyard Express is essentially a Mission-Pack Sequel with entirely different puzzles from the standard paid version. The only thing it lacks are Splitter Pieces and the Level Editor.
- Fusion Dance: What you have to do with the trains to decrease their numbers without failing the level. It also combines their colors into a secondary if the two trains are both a different primary color.
- Game-Breaking Bug: If you decide to view an author's full list of puzzles they created, in most cases the app will crash, and you will be stuck on the game crashing every bootup. The only way to fix this is to load this into the game, which will restart it from the title screen instead of a faulty Suspend Save.
- Level Editor: One was added in September 2011. It allows every feature from the main game, the only difference being that starting stations and goal stations can only spawn/have a requirement of up to 9 trains instead of 16.
- Post-End Game Content: Niagra Falls is considered the final main game city. Beat it, and you are given an ending screen and nine additional cities under "Bonus Puzzles".
- Sturgeon's Law: Heavily evoked with user-created levels. Many of them are incredibly simple and require little to no mixing or merging techniques at all. Some even don't require you to place down any piece of track to complete them. But for the ones of noticeably higher quality? They can be just as hard as the final levels in the main game, and in some cases even harder.
- Suspend Save: The game will allow you to return to solving puzzles from virtually any screen you exit out the app from.
- We Cannot Go On Without You: To solve a level, every train must survive without crashing.