To add moving AI traffic to an online Assetto Corsa server, run an AI-capable server such as AssettoServer, enable AI in cfg/extra_cfg.yml, place a track-compatible spline such as fast_lane.ai or fast_lane.aip in the server’s content/tracks/<trackname>/ai/ folder, and declare traffic cars in entry_list.ini. After joining through Content Manager and driving out of the pits, the server can spawn the configured cars.
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Traffic is not created by a client-only Content Manager switch. The server must load the spline and create the AI entries, while every player needs matching track and car content and compatible Custom Shaders Patch (CSP) and Content Manager versions.
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Prepare these items on the machine that will host the server:
- AssettoServer files: install or extract the server according to its current documentation. Keep the server installation separate from the normal Assetto Corsa game installation when following the documented setup.
- A compatible track layout: the layout must include an AI spline. Common filenames are
fast_lane.aiandfast_lane.aip. - Matching content: the server and every client need the same track layout and the cars used by the session.
- Compatible client versions: for the documented Steam-authenticated joining flow, use CSP 0.1.75 or newer and Content Manager v0.8.2297.38573 or newer.
- Text-editor access: you will edit
extra_cfg.yml,entry_list.ini, and possibly other server configuration files.
Check the track name and layout before copying anything. An AI spline is tied to a particular road network; a spline made for one layout should not be assumed to work on another.
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How Assetto Corsa server traffic works
In a normal offline session, the game can create AI cars from the local installation. Online traffic requires the server to perform that job. AssettoServer is a custom Assetto Corsa server implementation that can load one or more AI splines and provide AI traffic. The server reads the spline from the track content, creates AI entries from the server entry list, and synchronizes those cars for connected players.
That division explains the most common confusion: a track can show traffic offline while an online lobby remains empty. Offline mode may have a local AI configuration that the online server never sees. Conversely, a server can have AI enabled but still show no cars if its track folder lacks the correct spline or its entry list contains only human-driver entries.
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Keep the server files separate
Install or extract AssettoServer into its own server directory rather than mixing its files into the game’s main installation. This makes updates, backups, configuration edits, and troubleshooting easier, and it follows the current introduction’s installation guidance.
After extraction, identify the server’s configuration directory and content tree. The paths used in the documented setup are relative to the server installation:
cfg/extra_cfg.yml
entry_list.ini
content/tracks/<trackname>/The exact executable and launch method depend on the AssettoServer package and your operating system. Complete the basic server setup first, including a working player-car entry, before adding traffic. If the server cannot start a normal online session, AI configuration will not correct that underlying problem.
Confirm the server sees the intended track
Use the same track name and layout in the server configuration that you intend to select in Content Manager. Assetto Corsa content often has a base track folder plus separate layout identifiers. Copying a spline into the base folder while launching a different layout can leave the server with no usable path.
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- Assetto Corsa features an advanced DirectX 11 graphics engine that recreates an immersive environment, dynamic lighthing and realistic materials and surfaces.
- Extremely detailed with single player and multiplayer options, exclusive licensed cars reproduced with the best accuracy possible, thanks to the official cooperation of Car Manufacturers.
- ASSETTO CORSA has been developed at the KUNOS Simulazioni R&D office, located just inside the international racing circuit of Vallelunga, allowing the team to develop the game with the cooperation of real world racing drivers and racing teams.
Enable AI in extra_cfg.yml
Open the server’s cfg/extra_cfg.yml and add or change the AI setting to:
EnableAi: trueYAML is indentation-sensitive, so keep the key spelling and capitalization exactly as shown. Do not put the value in quotation marks, and do not add a second conflicting EnableAi line elsewhere in the file. Save the file, then restart the server so it reads the setting from a clean launch.
This switch only permits the server’s AI system to operate. It does not supply a driving path or create cars by itself. You still need a valid spline in the track’s ai/ directory and AI-designated entries in entry_list.ini.
Install the track’s AI spline
Use the server content tree
Navigate to:
content/tracks/<trackname>/ai/If the ai folder does not exist, create it with that exact lowercase name. Copy the spline supplied for the selected track layout into it. The documented beginner example uses either fast_lane.ai or fast_lane.aip:
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content/tracks/shutoko_revival_project/ai/fast_lane.aiThe folder name in the example is illustrative of the Shutoko Revival Project setup; use the actual folder name installed on your server. Do not rename a spline casually. If the track package supplies both formats, use the format expected by that package or guide.
Treat the spline and layout as a matched pair
A spline encodes a route through a specific road network. A file that works on one layout may cause cars to fail to spawn, stop in odd places, or behave unpredictably on another. The official default AI settings are tuned for Shutoko Revival Project, so other maps may require different settings. Start with a spline explicitly made for your chosen layout rather than attempting to reuse a Shutoko file.
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Check the server copy, not only your local copy
Copying the file into the client’s Assetto Corsa installation does not install it for the server. Verify the file exists under the server’s own content/tracks/ tree. If you run the server on another machine or in a container, perform the check there.
Add traffic cars in entry_list.ini
The entry list controls which cars the server creates. Keep at least one normal player entry, then add entries for cars intended to run as traffic. The beginner guide specifies AI=fixed for those traffic entries.
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A simplified pattern looks like this:
[CAR_0]
MODEL=your_player_car
SKIN=your_skin
DRIVERNAME=Player
AI=none
[CAR_1]
MODEL=traffic_car_model
SKIN=traffic_skin
DRIVERNAME=Traffic01
AI=fixed
[CAR_2]
MODEL=another_traffic_car
SKIN=another_skin
DRIVERNAME=Traffic02
AI=fixedUse the model, skin, and other fields that exist in your installed content. The important distinction is that the traffic entries carry the documented AI parameter while the player entry remains available for a human driver. Add as many valid traffic entries as your server and track configuration are designed to handle, but do not assume that increasing the count automatically improves performance or behavior; no general performance figure is established in the documentation.
Validate every referenced car
- Confirm each
MODELexists on the server and on clients. - Confirm each skin is present in that car’s content.
- Use unique driver names and entry sections.
- Check that the selected track layout has the spline used by the traffic entries.
If an entry references missing content, remove it temporarily and test with one known-good car. A minimal working list makes it easier to distinguish an entry-list error from a spline or networking problem.
Start a local test before opening the server to friends
Test locally first so that Internet routing does not obscure configuration mistakes.
- Save
extra_cfg.yml, the track’sai/folder, andentry_list.ini. - Restart AssettoServer and watch its console or log for startup errors.
- Open Content Manager.
- Go to Drive > Online > LAN.
- Select the configured player car and join the server.
- Drive out of the pits. In the documented workflow, traffic begins spawning after the player leaves the pit area.
Do not judge the result while your car is still stationary in the pits. If the server starts but no traffic appears after you drive onto the route, stop and check the AI setting, spline path, layout, and entry list in that order.
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Let players outside your LAN connect
A local test proves that the server and client can communicate on the same network; it does not make the server reachable from the Internet. For friends outside your home or office network, configure the host’s reachability and port forwarding according to your router, operating system, and server setup. The exact port values are configuration-specific and are not stated in the AssettoServer beginner guidance, so use the ports shown by your server configuration rather than copying an unrelated example.
Use an external invite or public listing
Generate the server’s external invite or use its public-list method after reachability is configured. A local-IP invite is useful only to people on the same LAN and will not provide an outside player with a route to your machine.
Check the complete joining chain
- Confirm the server process is running continuously.
- Confirm the router forwards the configured server ports to the host machine.
- Check that the host firewall allows the server process.
- Use the externally generated invite or public listing, not a private LAN address.
- Have every player install the same track layout, cars, and required versions.
If local players can join but outside players cannot, leave the AI files unchanged while testing routing. That symptom points to reachability or content compatibility rather than the spline itself.
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CSP and Content Manager compatibility
Custom Shaders Patch and Content Manager are part of the documented Steam-authenticated joining path. AssettoServer’s introduction specifies CSP 0.1.75 or higher and Content Manager v0.8.2297.38573 or higher for that flow. These are minimum compatibility versions, not a promise that every newer or modified build will behave identically.
Keep the server’s required client versions in your joining instructions. A friend who has the right track and cars but an older CSP or Content Manager build may fail authentication or be unable to use the server’s expected features.
Require a minimum CSP version when appropriate
The server FAQ documents a csp_extra_options.ini file for CSP server options and explains how to require a minimum CSP version. Use that mechanism when you need clients to meet a defined baseline, and communicate the required version before they attempt to join. A version requirement helps produce a clear compatibility failure instead of allowing clients with unsupported features into a session.
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Avoid checksum errors from CSP track-folder edits
If you use the CSP track-folder method, the FAQ gives a specific surface-name rule: change only the first surface entry from SURFACE_0 to CSPFACE_0. Changing additional surface entries can create client checksum errors. If a checksum mismatch appears after a CSP edit, revert the extra surface changes and leave only the first documented replacement.
Troubleshoot traffic systematically
No traffic appears at all
- Open
cfg/extra_cfg.ymland confirmEnableAi: true. - Confirm the spline is inside the server’s
content/tracks/<trackname>/ai/folder. - Confirm the selected layout matches the spline.
- Restart the server after every configuration correction.
- Join through Drive > Online > LAN and drive out of the pits before evaluating the result.
The server starts, but traffic cars do not spawn
Inspect entry_list.ini. Traffic entries must exist and use the documented AI=fixed parameter. Check each referenced model and skin, then test with one known-good traffic entry. An empty or incorrectly typed entry list can prevent cars from appearing even when the spline loads correctly.
Friends cannot join
Separate the problem into local access and external access. If LAN players can join, verify port forwarding, firewall rules, public-list settings, and the external invite. If nobody can join, first confirm the server is running and that clients have matching content and compatible CSP and Content Manager versions.
A checksum mismatch appears after CSP changes
Undo additional surface edits. In the documented CSP track-folder method, only the first surface entry should change from SURFACE_0 to CSPFACE_0. Restore the original names for later surfaces, restart the server, and have clients clear any locally modified copy if necessary.
Traffic behaves badly on a different map
Do not assume the Shutoko-tuned defaults apply everywhere. Confirm that the map has its own compatible spline, then adjust map-specific AI settings as required by that track. Test one layout at a time so a change for one road network does not mask a problem on another.
Self-hosting versus managed hosting
Self-hosting gives you direct access to the files that control AI traffic, but you are responsible for installation, updates, router configuration, firewall rules, backups, and troubleshooting. A managed service can reduce maintenance and port-forwarding work, but it is useful only if the provider explicitly supports AssettoServer AI traffic and permits the configuration changes you need.
| Decision factor | Self-hosted AssettoServer | Managed service |
|---|---|---|
| Configuration-file control | Direct control of extra_cfg.yml, entry_list.ini, AI files, and CSP options. |
Depends on the provider; the available control is not stated without checking its plan and panel. |
| Custom AI splines | You can place compatible splines in the server track folder. | Must be explicitly supported; availability is not stated without provider verification. |
| CSP options | You can manage documented server-side CSP files yourself. | Depends on whether the host exposes those files or settings. |
| Port forwarding | You configure and maintain it. | Usually handled by the service, but the exact networking arrangement is not stated. |
| Maintenance | You handle updates, logs, backups, and recovery. | The provider may handle infrastructure maintenance; responsibilities vary and are not stated here. |
| Player capacity and network performance | Limited by your hardware, connection, and configuration. | Depends on the provider’s allocated resources; no independent performance figure is established. |
Before paying for a managed service, ask specifically whether it supports AssettoServer, server-side AI traffic, custom track AI folders, entry_list.ini editing, and the CSP version policy you intend to use. “Assetto Corsa hosting” alone does not prove that AI traffic is available.
Maintenance checklist for a reliable traffic server
- Back up
extra_cfg.yml,entry_list.ini, and the server content tree before changing them. - Record the exact track layout and spline filename used by each server.
- Keep a copy of the client CSP and Content Manager minimum versions in your joining instructions.
- After changing a track, spline, car, or CSP option, perform a LAN test before inviting outside players.
- When troubleshooting, change one variable at a time and restart the server after configuration edits.
- Remove broken traffic entries rather than leaving references to missing models or skins.
The dependable configuration is therefore a chain: an AI-capable server, EnableAi: true, a spline matched to the selected layout, traffic entries marked AI=fixed, compatible client content and versions, and a reachable network path for players outside the LAN. Breaking any one link can leave an otherwise correctly installed server without visible traffic.
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