Music on iPhone cutting out while driving.

Hello UsernameNoWork,

Thanks for choosing the Apple Support Communities. We see you're having issues getting Apple Music to play in low-signal strength areas. We can help.

You have the option to download music for offline listening. To do that, try following:

Add music to iPhone and listen offline - Apple Support

"Download music from Apple Music to your iPhone

• Download a song, album, or playlist: Touch and hold music you’ve added to your library, then tap Download.
• After you’ve added a playlist or album, you can also tap  at the top of the screen.
• Note: You must turn on Sync Library to download music from Apple Music to your library (go to Settings  > Music, then turn on Sync Library).
• Always download music: Go to Settings > Music, then turn on Automatic Downloads.
• Songs you add are automatically downloaded to iPhone.
• See download progress: On the Library screen, tap Downloaded Music, then tap Downloading.

Note: If the music you’re downloading is available in Dolby Atmos, the Dolby button  appears next to the item, and you can download it either in Dolby Atmos or in stereo. To download music in Dolby Atmos when available, go to Settings  > Music, then turn on Download in Dolby Atmos. See Listen to Dolby Atmos music on iPhone."

We hope this helps.

Cheers!