The more you play Trainyard, the more you realize that there are a handful of common track forms that you end up using again and again. In the next few sections, I wanted to start a catalogue of these forms and when they're useful. If you're still reading, then there's a good chance you've seen some or all of them already, but maybe we'll discover something interesting about them as we go. This will also give me a chance to name them, an honour I hope I can live up to.
Let's start with "The Molehill". This one's a classic - one of the first little tricks you learn. We've already seen it used in the section on Axiom #2, but I'd like to point out some of its interesting features. Its purpose is to merge two cars that are two squares apart on the same line of track. Here's a simple example:
Molehill has an interesting variation that can come in handy when you've got more than two cars along the same track, each separated by two squares. In the examples below, the change in the intial state of the first leg of the Molehill (up/down) changes which cars merge. With the 'up' initial state (first example), you end up with one green car and one orange. However, the 'down' initial state (second example) effectively skips the first car, resulting in two yellows and one purple. In other words, you can change this square to shift between a 1+2, 3+4, 5+6 merge pattern and a 1, 2+3, 4+5, etc merge pattern.
The Molehill won't work if there is one out-of-phase car between two in-phase cars, because the middle car will reset the first switch, causing cars 1 and 3 to take the same path:
The solution is to use a Phase Filter to separate the in-phase and out-of-phase cars:
Next we'll take at the easiest way to merge cars separated by four squares instead of two.
Next: The Loop