About a week ago, we reported Android Auto would receive a bunch of new features, including a new privacy mode and in-car games. A split-screen mode was also in the making, which has now rolled out to users.
The new mode is available for cars with a widescreen view, which lets you display two apps at the same time without having to switch back and forth between the two. The main app is displayed on the left side of the screen, as it would have appeared previously, while the right side of the screen now shows another app in a smaller box. If you're showing the map in the secondary view, it will look like you're using Maps on your phone in portrait mode.
The most common layout would be to show navigation and music at the same time. Sadly, not all apps support this view, as some users have reported they couldn't use it with Waze. There also doesn't seem to be a way to display an app in full screen, meaning you'd always have to stick with two windows at the same time.
As the feature is new, Google might improve it in the coming months and allow users to customize the layout or de-activate split-screen view entirely.