From reading the Magic Earth FAQ, I believe the user data actually isn’t used for traffic at all (at least the manually reported events certainly aren’t).
Edit: never mind I missed a later part in the FAQ:
Do you share data with third parties?
We send position data to our traffic provider to generate real-time traffic information. The data is anonymized on the phone, using a changing key (so it’s not linked to you), and it is deleted after 5 minutes.
Magic Earth (while not FOSS, it’s privacy oriented though) can do this.
There’s also Transportr, but AFAIK it’s been unmaintained for quite a while now, so it may not work / stop working soon.