Driving is serious business—you're in control of a rolling pile of metal and glass weighing thousands of pounds, and one moment of inattention can have very messy consequences. So, for goodness' sake, don't screw around with your phone while driving. Google Maps has voice commands while in navigation or driving mode to help you keep your hands off the phone, and today there are a lot more available.
Google's blog post goes through the whole process of setting up OK Google commands to work in Maps. If you have OK Google turned on for all screens, it'll work in Maps by default, but you can also choose to only have it active then. For some reason, Google uses finding a gas station as an example in the post, but that's one of the few commands that was on the list before. Here's everything on the updated list of supported navigation voice commands.
Directions and travel
"Mute." or "Mute voice guidance."
"Unmute." or "Unmute voice guidance."
"Show traffic." or "Hide traffic."
"Show satellite." or "Hide satellite."
"Navigate home." or "Navigate to Starbucks."
"Show route overview." or "Show alternate routes."
"What road is this?"
"What’s my next turn?"
"What's my ETA?"
"How's traffic ahead?" or "How's traffic to home?"
"What's the weather like?"
"Avoid tolls." or "Enable tolls."
"Avoid highways." or "Enable highways."
"Avoid ferries." or "Enable ferries."
More commands you can say
"Find gas stations." or "Find restaurants."
"Send a text to Larry." or "Send a SMS to Sergey, I'm feeling lucky."
"What's the weather like?" or "How's the weather in Seattle?"
"Play some jazz." or "Play happy birthday on Google Play Music."
"What's the closest hotel?"
"When's my next meeting?"
Previously, the supported commands included mute, next turn, ETA, find gas stations, and exit/resume navigation. The newly added commands don't appear to be live yet on my end. There's either a server-side or app update needed to get them working.