> ## Documentation Index
> Fetch the complete documentation index at: https://dcc-5ccd5152.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# BigFred Core Concepts: Layouts, Vehicles, Trains, and More

> Understand layouts, vehicles, trains, command stations, interlockings, leases, and user roles in BigFred — everything you need before your first session.

BigFred organises everything around a small set of concepts that map closely to how real model railroad sessions work. Understanding them upfront will save you time and help you get the most out of the system.

<Accordion title="Layouts">
  A **layout** is the top-level container for a modelling session. It groups together a set of command stations, interlockings, and the operators who are currently active. You pick a layout on the login form, and your session is tied to that layout until you log out.

  Admins create and manage layouts. A layout can be **locked** to hide it from the login dropdown — useful when a layout is being set up or torn down. One special **system layout** always exists as a fallback and cannot be deleted.

  If you're running a one-off home session, you'll almost always use a single layout. At club events, the admin typically creates one layout per physical room or module group.
</Accordion>

<Accordion title="Vehicles">
  A **vehicle** is a single locomotive, EMU, motorized wagon, driving trailer, or trolley that you register in BigFred. Each vehicle belongs to your account and carries a **DCC address** — the number the command station uses to send speed and function commands to the decoder.

  * **Short addresses** span 1–127.
  * **Long addresses** span 128–9999.

  Use whichever range matches your decoder's programming.

  Vehicles without a DCC address are called **dummies** — they can be added to consists and to the layout roster for display purposes, but the throttle never sends DCC packets to them. A dummy is useful for unpowered wagons that travel with a locomotive as a set.

  Your vehicles live in **My Vehicles**. To drive one on a layout, you first add it to the layout roster from the **Fleet → Vehicles** page.
</Accordion>

<Accordion title="Trains (Consists)">
  A **train** is an ordered group of two or more vehicles driven as a single unit — what DCC calls a consist. When you move the speed slider on a train, BigFred fans the speed command out to every member vehicle.

  Each member in the consist can be configured individually:

  | Setting              | Effect                                                                         |
  | -------------------- | ------------------------------------------------------------------------------ |
  | **Speed multiplier** | Scales the target speed for this member, compensating for decoder differences. |
  | **Reversed**         | Drives this member in the opposite DCC direction, for back-to-back coupling.   |
  | **Start delay**      | Staggers the speed command so long consists accelerate smoothly.               |

  Create and manage trains under **My Trains**. Like individual vehicles, trains must be added to the layout roster before you can drive them.
</Accordion>

<Accordion title="Command Stations">
  A **command station** is the physical DCC hardware that puts packets on the track. BigFred supports three families:

  | Type                       | How it connects                                    |
  | -------------------------- | -------------------------------------------------- |
  | **Roco / Fleischmann Z21** | UDP over Wi-Fi or wired LAN                        |
  | **LocoNet (serial)**       | USB-to-serial adapter (e.g. Digitrax PR3, MS100)   |
  | **LocoNet (TCP)**          | Network gateway such as JMRI or an lbserver bridge |

  One layout can have multiple command stations attached — for example, a Z21 for one module group and a LocoNet bridge for another. When you open the throttle, you choose which command station to drive through.

  Each command station can also be configured to accept **inbound remote throttle connections**: physical Z21 handsets can connect via UDP, and WiThrottle-compatible apps can connect over TCP. Your admin enables and configures these inbound servers per command station.

  Command stations are configured by admins under **Admin → Command Stations**.
</Accordion>

<Accordion title="Interlockings">
  An **interlocking** represents a logical signal box — a station throat, a junction, or any entry point where train movements need to be coordinated. At most one operator occupies an interlocking at a time.

  When you **join** an interlocking, you become its signalman for that session. Drivers who want to enter your block radio you through the interlocking's chat channel, and you supervise their movements. Leaving the interlocking releases the occupation so another operator can take over.

  You can see all interlockings and their current occupants on the **dashboard home page**. Click any interlocking row to enter it.
</Accordion>

<Accordion title="Leases">
  A **lease** lets you temporarily hand driving rights for one of your vehicles or trains to another operator — the borrower. The vehicle stays owned by you, but the other operator's throttle can control it for the duration of the lease.

  When you create a lease you can optionally set a **speed limit** (as a percentage of maximum speed) to keep the borrower from over-revving your model.

  Leases appear under **Rentals** in the navigation. You can revoke a lease at any time.
</Accordion>

<Accordion title="Roles">
  BigFred has two permanent account roles:

  | Role       | What they can do                                                                             |
  | ---------- | -------------------------------------------------------------------------------------------- |
  | **Driver** | Register vehicles, drive on layouts, join interlockings, create leases.                      |
  | **Admin**  | Everything a driver can do, plus manage layouts, users, command stations, and interlockings. |

  There is also a layout-scoped **signalman** role. Admins can permanently grant the signalman role to specific users on a layout. Users can also self-promote to signalman within a layout by entering the layout's admin PIN — this is a permanent grant for that layout, not a timed window.

  **Temporary admin elevation (sudo)** lets a driver perform a one-off admin action without a permanent role change. You enter the layout's admin PIN, and BigFred elevates you to admin for **2 minutes**. After the window expires your role returns to driver automatically. Use this to, for example, add a command station mid-session without needing a separate admin login.
</Accordion>

<Accordion title="DCC Address Pool">
  Each user account has a **DCC address pool** — one or more address ranges that the admin allocates to you. When you register a vehicle, BigFred checks that the DCC address you enter falls within your pool. If it doesn't, the registration is rejected.

  This prevents address conflicts between operators at shared layouts. Admins set and adjust pools from the user management screen (**Admin → Users**). You can see your own pool allocation at **Account → Profile**.

  Dummy vehicles (no DCC address) bypass the pool check entirely.
</Accordion>