How do I prevent Music app from using 1 GB of cellular data in less than 10 minutes?

I received 3 text messages within 10 minutes from my cellular carrier as I was driving in my car with iTunes Radio streaming music. The first message said I used up 65% of my 1 GB plan. The next said 90%. The last said 100% and I would be charged $20 for going over.

I went into Settings > Celluar to find the culprit. It was indeed caused by the Music app, so I immediately switched off its cellular usage. It had used up 1 GB in 10 minutes (this was the first time I attempted music streaming while driving). It was most likely the iTunes Radio inside the Music app. I have zero music files in my collection, so the data usage couldn't have arisen from synching with iTunes.

In all the articles that I've read, they say iTunes Radio should only use 28 MB per hour - much less than what I just experienced. So what caused my meteoritic rise in data usage?