Well to be honest I think no matter whether its standard in-game cars or not, Civs usually stick out anyway due to how actual players drive vs the AI on set paths, but I mean I think civs shouldn't really need to blend in with the AI traffic in the first instance as their not always doing something wrong, that being said seeing some UK cars either in the Civ garage or replacing some of the traffic models (if thats possible) with UK types of cars would be pretty cool as Caelum suggested.