• Trainz 2009 must be installed beforehand (see Get a Free Copy of Trainz 2009 and Installing Trainz 2009)
• If you are using an NVIDIA graphics card: Please follow this guide beforehand
• The game should be launched briefly once (optional)

About 50GB of free space is required for the full installation (Trainz + U-Bahn Sim Berlin expansion).

• Trainz Simulator 2009*
• Trainz Simulator 2010*
• Pro Train Perfect 2 (missing dependencies must be installed afterward (see ptp2))

• Trainz Simulator 12 (may work, but not recommended)

• T:ANE (Trainz A New Era)
• Trainz Simulator 19
• Trainz Simulator 22
  

* Build 44653 or higher recommended

The U-Bahn Sim Berlin installer can be downloaded from the Download section.
Once the installer is opened, you will be greeted by the start screen.
Click “Zur Installation →” (EN: Continue to installation) to begin.

First, you’ll be taken to the standard settings page.

Ideally, the Trainz installation path is already filled in.
If not, you can select it via the “Ordner auswählen” (EN: Select folder) button.

Next, you can choose which method you want to use to install U-Bahn Sim Berlin.

With a fast internet connection or a slower PC, the “Unkomprimierte Version” (EN: uncompressed version) is recommended.
It is larger to download but allows faster file processing.

With a slower internet connection, the “Komprimierte Version” (EN: compressed version) is recommended.
It downloads faster, but installation takes a bit longer since the files need to be unpacked.

The total storage usage in the end is the same for both versions.
Only during installation the space in brackets (in addition to the ~50GB) is required on the hard disk C:\.

By clicking “Zusätzliche Optionen anzeigen” (EN: Show additional options), you can enable extra features.

• Weichensound-Patch installieren (EN: Install switch sound patch): Removes Trainz's default switch sounds and plays only the U-Bahn switch sounds. A before-and-after comparison is shown in this video.

• Texturen herunterskalieren (EN: Downscale textures): Installs a version with downscaled textures, as the name suggests. This allows U-Bahn Sim Berlin to run smoothly on lower-end PCs.

• Freie interne Kamera aktivieren (EN: Enable free internal camera): This adds the -freeintcam option to the trainzoptions.txt file. It allows you to freely move the camera inside the cab using the arrow keys.

• Ab Revision nur installieren (EN: Install from revision only): Updates are released in the form of revisions.
  This option lets the installer install only content released since revision XXXX.
  It’s useful if you want to reinstall a faulty update, for example.

• Maximale Anzahl an Downloads begrenzen (EN: Limit maximum number of downloads): This lets you define how many assets are cached simultaneously on your drive.
  If disabled, all packages are downloaded and cached without delay.
  After an asset is installed, it’ll removed from the cache.
  For example, if enabled, only 5 assets will be downloaded first.
  Only when the first asset is installed and removed from the cache the next asset will be downloaded.
  This option is highly recommended for users with very limited free space on drive C:\.

If your computer has an NVIDIA graphics card, the installer will display the following warning:

For more information about this warning, please refer to this site: Issues with NVIDIA Graphics Cards

Additional steps are necessary after installation to ensure the modification runs without problems.
These steps are explained here: Steps after installation