Cosmetic stop-and-go background traffic for URP: self-filling lanes of bumper-to-bumper cars that creep, brake, and ripple in realistic go/stop waves.Requires URP. Built and tested with Unity 6000.3 + URP 17.3.No custom shaders included. The demo materials use URP/Lit and import as magenta under Built-in RP or HDRP. The optional per-car tint sets _BaseColor and relies on the SRP Batcher.The traffic simulation is pipeline-agnostic and runs anywhere once you supply your own materials. HDRP untested.Ambient Traffic Jam drops a living, cosmetic traffic jam into any scene. Cars pack bumper-to-bumper in lanes and follow the car ahead — accelerating to close a gap, braking to a safe stop — while flipping between random go/stop phases, so pauses ripple backward as real stop-and-go waves. A camera-anchored window keeps the belt full: cars that fall off the rear edge are recycled to the front, so the jam never "ends" and the live car count stays bounded no matter how far the player travels.It's built to be pure background dressing: no colliders during normal play (zero physics cost), and every bit of randomness comes from a private RNG, so it never disturbs a seeded/deterministic gameplay RNG. Per-car body colour is applied with shared material variants (not per-object property blocks), so every car stays SRP-batched — variety with no extra draw calls.Fully data-driven and customisable: add as many lanes as you like, set each lane's position, side and crawl speed, drop in your own car/bus/truck prefabs, tune jam density, stop timing, colour palette and engine-audio, and optionally wake impact colliders around a target (e.g. on player death) via a single call. Great for endless runners, city drivers, top-down and isometric games, or any scene that needs believable idle traffic.Includes a ready-to-use URP demo scene with original low-poly vehicles and engine-loop audio, plus a full PDF manual. Requires Unity 6000.3+ and the Universal Render Pipeline.• Self-filling lanes — assign positions + prefabs; each lane auto-packs bumper-to-bumper from a mix of your vehicles (no car-count to tune)• Realistic stop-and-go — car-following with accel/brake and randomised stop phases, so the line surges and stalls in backward-travelling waves• Camera-anchored recycling window — endless jam with a bounded, capped number of live cars• Per-car colour tint from a weighted palette, via shared material variants → stays SRP-batched (no extra draw calls)• Looping, distance-gated engine SFX — each car fades its bed in while creeping, out while stopped, with an earshot cutoff• Optional impact colliders — off by default (zero physics cost); wake them near a target on demand• Deterministic — private RNG only; never disturbs a seeded gameplay RNG• Clean, documented C#, assembly definitions, a URP demo scene, and a PDF manual• No external dependenciesThe C# scripts in this package were authored with the assistance of an AIcoding assistant (Anthropic's Claude, via Claude Code). All code was reviewed,edited, and tested in the Unity Editor by the author before release.No other package contents were AI-generated: the 3D vehicle prefabs, materials,and the demo scene are built by hand from Unity primitives, and the demoengine-loop audio is produced by a custom procedural DSP script (not agenerative-AI audio model). No third-party AI-generated art, audio, models,or datasets are included in the package.
