Is "however" redundant?

Yes. It is unnecessary.

It depends on the context. With the sentence standing alone it isn't necessary. But if the sentence were following a discussion about the difficulties of getting people to wear seat belts, you could use the "however" to indicate a contrast.

Here's an example:

Nearly everybody cheered wildly at the end of the concert, however, there were a few people who were obviously disappointed.

I'll accept what has already been said about the "however."

However, the "to not wear rear seat belts" should be mentioned.

"To wear" is an infinitive. One can split it (interject a word between the "to" and the object verb), but in "formal writing" one should not do it.

This kind of writing is a form of formal writing.

The wording more properly should have been, "not to wear rear seat belts."

“Continue to” is a phrasal verb so I don’t have a problem with the “continued to not wearing ...”

Many thanks for your replies.