Google Maps does give you an option to download maps for a given area to your phone, which theoretically would avoid data use while you're driving. At the same time, though, I'm not certain it will default to using the stored data, instead of getting current data online, when it does have access to a data signal. It's possible you'd need to turn off Mobile Data in order to have it use the stored data. And you'll need to keep your data on, I believe, or Android Auto in general won't work.
Also, the stored data is automatically deleted after 30 days, so you'd need to keep on top of this.
Just a few thoughts for you to consider, if you need to tightly manage your data usage.