The standalone version of Driving Mode isn’t to be confused with the Driving Mode feature built into Google Maps, which automatically boots up once you start navigation. As Esper’s Mishaal Rahman points out, Google added Assistant Driving Mode to Maps before it even released the standalone Driving Mode.
The only difference between the two is that you can access the standalone version by saying a voice command like “Hey Google, launch Driving Mode,” or by tapping the Driving Mode