A new simulation has come, called Outerra! It is the most realistic simulation as it has an engine which recreated the whole world, with ground vehicles to cruise and airplanes to jet in the sky, there are roads, train tracks, ship, quarry, climates changes etc, this simulator website is: http://outerra.com/
You can see a test video, it is on building but it is still highly detailed in beta, it is gonna be released in the future, the date is still not set.