You've always been able to run the Android Auto app on your phone to get a better/safer interface while driving, but Google doesn't widely advertise that functionality (the Auto app is mainly used for connecting to car entertainment systems), and it doesn't always work correctly. Google announced a replacement over a year ago at Google I/O, and it's finally showing up on phones.
Google Assistant's Driving Mode was first revealed at Google I/O 2019, but the company has been relatively silent about it since then. Driving Mode was intended to switch the phone to a minimalist interface with a single voice command, with a home page containing shortcuts to navigation, calling, music playback, and other options. Google later said Driving Mode would replace Android Auto's on-phone mode, though the company initially said the transition would take place "in the coming months," which didn't quite pan out.
The original incarnation of Driving Mode
Earlier this month, it started to look like the long-awaited Driving Mode could end up as a feature inside Google Maps, rather than the app-independent approach of Assistant or Android Auto. It appears that functionality is being rolled out to more people, though it's still unclear if it's a limited test, or if Google intendeds to ship this to everyone in the coming weeks. Our friends at XDA Developers say several of their phones have the new mode enabled, but it has yet to show up on any of my devices.
The new Driving Mode is accessible by tapping your photo in the Google Maps app, pressing on 'Navigation settings,' and finally selecting 'Google Assistant settings'. This menu previously took you to the general Assistant settings screen (the same one accessible through Google Home, Search, etc.), but now it brings up a new panel for Driving Mode. You're supposed to be able to say "OK Google, let's drive" to bring up the new interface, but even for people with Driving Mode, that doesn't appear to work yet.
Driving Mode (Source: XDA Developers)
In its current incarnation, Driving Mode adds a bottom toolbar to Google Maps with an Assistant button, a button to scroll through supported apps, and media controls. The general design is similar to Android Auto, but the controls are moved around to better suit the aspect ratios of phones.
Keep an eye out for the new Driving Mode as it (possibly) starts to reach more phones. Here's hoping Google eventually unties it from Maps, so you can use alternative mapping applications like Waze.
- XDA Developers