Traffic Features

Traffic cars obey intersections

When an intersection has a light program authored in the Traffic Editor, traffic cars respect it. A car arriving at a red light slows and stops inside the intersection entry zone; it waits for green; then it accelerates across. At intersections without a light program, cars use right-of-way rules driven by the lane priorities the track author set — a car on a Main road keeps going, a car on a Secondary road waits for it to clear.

Just Floor It — don’t wait for no reason

Intersections in the TrafficTool are not always full junctions with lights and cross-traffic. They are also used simply to connect one lane to another so cars can flow from segment to segment. Stopping at every connection would be absurd.

The Just Floor It behaviour handles exactly this case. If an intersection has no reason to wait — no cross-traffic, no red phase, no conflict with another lane — cars drive straight through without slowing down. They only stop when there is an actual reason to yield. The result: traffic flows smoothly across stitched-together lane networks, and genuine junctions still behave like junctions.

Different lanes can have different speeds

Every lane carries a speed limit set by its role (Highway, Main, Secondary, Parking). Cars on a Highway lane cruise at full highway speed; the same car spawned on a Secondary lane respects the slower limit. That is how one map can feel like a mix of boulevards, side streets and motorways rather than a single uniform speed.

On top of the lane’s base speed, the simulator additionally slows cars through curves. The tighter the corner, the more the effective speed is reduced. That is why traffic visibly slows into a switchback and accelerates out of it, without any author-placed speed zones.

Traffic follows the car ahead — smoothly

Every traffic car continuously monitors the car directly in front of it. If the gap closes below a target following distance, the car brakes to match the leader’s speed; if the gap opens up, it accelerates back to its lane’s limit. The transition is smooth, not binary.

Under normal conditions the fleet does not clump. Keeping traffic flowing without stop-and-go waves is a core fix in the TrafficTool — cars modulate their speed gradually rather than overreacting to each other. Jams only happen for real reasons: a car is forced to brake unusually hard, the player causes an accident, or an intersection backs up. Once the cause clears, the flow recovers on its own.

How traffic cars react to the player

Traffic is not a static obstacle field. Cars read your driving and respond to it in several distinct ways.

Horn — they accelerate out of the way

Hold the horn for roughly a second on a car directly in front of you and it will briefly accelerate. The tool reads this as the classic “get out of my way” gesture — the car pushes forward for a short window, widening the gap so you can pass cleanly.

High-beam flash — they can change lane

Flashing your high-beams at a car directly in front is another overtake signal. A traffic car that notices the flash may change lane to let you by. Not every car reacts every time, but the behaviour is there, and it is one of the subtler ways the tool acknowledges the player.

Tailgating — they move aside

Sitting close behind a traffic car for a sustained period also registers as “I want past”. The car will often change lane automatically to clear the way, even without you touching the horn or the high-beams. A gentle form of real-world courtesy baked into the AI.

Being overtaken — they may honk or brake slightly

When you pass a traffic car closely or aggressively, it can react — a horn blast at you, or a small brake as the other driver flinches. This keeps overtakes feeling consequential rather than silent.

Brake-checking — they honk at you

Brake hard in front of a traffic car with a short gap and there is a chance it honks at you as a protest. It does not swerve or try to crash you — it is an audible reaction that adds life to the road.

Race Cars mixed into traffic

A subset of the traffic fleet behaves differently from the rest. Race Cars — when the Race Cars feature is enabled — spawn into normal traffic looking the same as any other car, but with a more aggressive personality:

• They drive faster than the lane’s civilian pace.
• They overtake other traffic cars on their own, without any input from the player.
• You can challenge a Race Car to a duel by driving alongside it and pressing the horn three times.

Because they share the same model library as the rest of traffic, you cannot tell a Race Car from a normal car at a glance — until it starts behaving like one. Full details, including how untriggered Race Cars behave differently from engaged ones, are in the Race Cars chapter.

Autonomous lane changes

Lane changes happen for several reasons. The ones in the player-reaction section above (horn, high-beam flash, tailgating) are all technically lane changes too — they are just triggered by you. Beyond those, the AI performs lane changes on its own in these situations:

• Intersection re-routing. If the lane ahead is blocked at an intersection and a parallel lane offers a free path, the car moves over.
• Race Car overtakes. Race Cars in the mix actively change lane to pass slower traffic, regardless of whether the player is nearby.
• Police Car overtakes. Police cars in pursuit, or merely navigating through traffic on their way to the player, have their own overtaking logic and will change lanes to get through denser traffic. The behaviour can be tuned in the police settings — see the Police Chases chapter.

The Allow Lane Changes toggle in Quick Settings gates all autonomous lane changes, including those triggered by the player. Turning it off locks every car to its spawn lane — useful for hot-laps where an AI drifting across your racing line is frustrating. Leave it on for anything cinematic.

Collision avoidance with the player

Traffic cars are not hyper-reactive to the player. When you come close to a traffic car — overtaking, merging, threading through — it does not immediately slam the brakes. Instead the AI has a short reaction window during which it lets you pass. The idea is that most close passes are intentional moves by a fast-moving driver, not accidents, and a car that panic-brakes at every fly-by would ruin the flow.

Emergency braking does still happen, but only when it must: when the gap collapses below the safe limit and a collision would otherwise be certain. The typical experience is therefore that traffic gives you room, tolerates close passes, and only brakes hard when the geometry actually demands it.

What happens after a crash

A traffic car involved in a serious crash stops driving and is eventually cleaned up by despawn. The visual and physical side of what that crash looks like — dented panels, fire, explosions — is handled by the deformation system; see the Deformation Physics chapter for how severity scales with the impact.

Panic Driver — light crashes, different outcome

For lighter incidents — crashes where the car does not deviate too far from its original position and is still physically capable of driving — the AI can flip into a special mode called Panic Driver. Instead of stopping, the car goes into a short burst of panicked acceleration and continues through traffic for a while, broadly similar to how a Race Car drives when engaged.

The effect is that minor contact does not always produce a dead wreck on the road — sometimes the other driver just bolts. It adds an element of unpredictability to accidents: you expect the car to stop, and it takes off instead.

License plates

With License Plates on, the tool generates region-appropriate plates for spawned traffic cars using the plate style assigned to the active car list (European, USA, Japan). Plate text is randomised, but the format follows that region’s real-world conventions. Because traffic cars only exist briefly in view, this small touch adds a surprising amount of realism for a modest cost.

The feature is flagged experimental because some car mods have unusual plate mesh positions, which can cause the generated texture to sit awkwardly. If you notice artefacts on a specific mod, either disable the feature or fix that car’s plate setup in its mod files.

Online traffic

On multiplayer servers, traffic has to be synchronised across clients or it turns into ghost cars that collide for some players and not others. The Enable Online Traffic toggle opts you into whatever synchronisation the server allows. Features that conflict most with sync — Race Cars, Police, Extra Cars, Deformation Physics — are labelled experimental online for this reason; expect occasional visible desync between clients when several are active at once.

Show Other Players decides whether other human-driven cars appear inside the TrafficTool’s walking-mode view. It does not affect normal driving — only the in-world pedestrian / phone scenes.

Troubleshooting

Traffic stops at every intersection, even pointless ones

Confirm Just Floor It is behaving as expected — intersections without cross-traffic or a red phase should not stop cars. If they do, the junction is configured with a light program or yield rule that needs adjustment in the Traffic Editor.

Traffic slows for no reason

You are probably in a curved section. The simulator automatically reduces speed through corners.

Horn does nothing

Hold it for at least a second on a car directly in front of you. Three quick presses while alongside a Race Car triggers a race instead.

Traffic never moves aside when I tailgate or flash

The reaction is probabilistic and needs a sustained action. Also confirm Allow Lane Changes is on — without it no autonomous lane change can happen.

A crashed car stays on the road forever

Crashed cars are cleaned up by despawn after they fall behind you or their timer elapses. Drive on and come back.