A couple of months ago, Microsoft updated its Windows 10 Mobile Maps app for Insiders with Bluetooth audio capabilities. Following suit, the update is now rolling out to all Windows 10 users, not just those in the Fast Ring.
The Bluetooth audio feature makes getting directional cues much easier while driving and with higher quality. The update is most noticeable in the settings first with an option to play voice navigation 'Over Bluetooth (when available)' to the car's speakers. Also, there are three settings for the Bluetooth volumes ranging with 'Softer','Normal', and 'Louder' options.
If you check your phone, the update should be available already. If not, check out the update by downloading the Windows 10 Mobile Maps app from the Windows Store via the link below.