In the original game, all railway station had to be rectangular, with all tracks in the same direction and with the same length. With the irregular stations feature, arbitrarily shaped stations become possible. Platforms can have varying lengths and point in different directions. Combined with new graphics sets very realistic and complex station layouts are possible.

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These examples are not about signalling, so nothing much is noted about the signalling aspects of these stations. In general, signalling for irregular stations works in the same way as for regular stations.
Irregular station
TTDPatch OpenTTD

One example for irregular stations, using platforms of various lengths and combining terminal and through platforms. The waypoint is necessary so that the trains will not accidently head towards the through platforms to the left.

Irregular station
TTDPatch OpenTTD

Using irregular stations, some setups can be built smaller than before. In this example, one square is saved on each side of the station, compared to a station with the same platform length. It can also be seen the other way around: Using the same space as before, the platforms are extended by one square.

Irregular station
TTDPatch OpenTTD

Through station making use of irregularity, developed by Rob from the tt-forums. Again, it mainly saves space compared to the rectangular station with the same platform length.

Irregular station
TTDPatch OpenTTD

This is one(!) station! Layouts as this one can be achieved by using the new demolishing routines that come with irregular stations. Instead of deleting the whole station, you can now blow up each platform separately. This station was built with four platforms, then the two in the middle were deleted and replaced with normal track.

Irregular station
TTDPatch OpenTTD

Since it is possible to build on slopes, this station can be build in the same way. The platforms on the lower level are built first, then one intermediate platform is added on the slope, and finally the two platforms on the upper level are built. The intermediate platform is then deleted to make room for the tunnel entrance.

Irregular station
TTDPatch Not in OpenTTD

In order to prevent long trains going to platforms that are too short, entry to these platforms can be restricted. In this example, the signal in front of the short platform has a restriction "Number of train carriages <= 8", because 8 carriages exactly fit to this platform. The other platforms are not restricted, because shorter trains can use them just as well. To reserve these platforms for longer trains only, one can place a restriction like "Number of train carriages > 8".