As already announced elsewhere, I've been busy over the last days coming up with a support effect for the OSM2City generated detailed roads. This actually is pretty neat now and should cover most cases in terms of configurability.
Here's how it looks at the moment - cars are basically painted as simple blocks, the shader just assigns a random color, the headlights are procedurally generated as lightmaps. Since this is Scandinavia, we keep headlights on during the day, I'll add an option to have them off when it's light for other parts of the world.
At night you get road illumination and traffic density modulated by road type - there's less traffic on secondary roads. Also car speed varies, it's usually faster on the main roads.
If you start to increase traffic density, it'll slow down where it gets heavy, eventually grinding to a halt on the highway whereas it continues to run on the secondary roads (looks a bit nicer on video...)
The effect Effects/road.eff is on FGData but won't do anything because currently the OSM2City generated data doesn't request it - so to see anything, the effect requested for roads needs to be patched to ask for the new one.
With the traffic patterns running more or less, I could use some help from texture artists. What can be done is to render car images from above rather than the generic blobs - for that I'd need such pics on a strip (pretty much like we do for trees).
What can also be done is that if we can get heightmaps for the cars, we can render them mock 3d (pretty much like the urban shader effect generates a relief from the urban textures) - that won't hold from close distance, but look sort of okay from higher up.
Also, at this point some input on what ought to be configurable where (runtime/design time/hard-coded/...) would be good.