It sounds like the game is inaccurate in how it models traffic, because in real life people do move out to make use of empty inner lanes (outer lanes? I can never remember). NB: I've not played the game so I'm not 100% on what the traffic problem is, exactly.

The problem stems from the car AI being crazy aggressive in it's lane switching. They will switch to the lane for their exit the instant they can, even if they still have to travel around the entire city to get to it. Leading to middle lanes not getting as much use (At least without careful planning to ensure there is something they can exit the road from the middle lanes with) and potentially large backups of a single line of cars waiting to turn right (Even when the lane right next to it is also a right turn lane). They also cannot merge properly so I end up placing exits on both side of my highways (For both incoming and outgoing traffic) with one side coming up and over the road to join into the other sides exit to limit congestion.

Not that any of these things are completely unrealistic but it is occasionally annoying when your traffic is backed up solely because they're ignoring the adjacent lane.