1. Night and day cycle.. let the user choose what ratio he likes (for example, 1 day = 6 hours, etc.)
and also the option to change the weather. (like morning to evening would be humid, and in night time, raining, something like that)
2. Add a part of the city where you can see an ocean/beach while driving. I can imagine how refreshing it is to see a beach while in long hours of driving