As well as human hearing, human touch, human balance / proprioiception, possibly even smell too.

If a person is rear ended, they might not even see the car that hit them, but they know they're hit based on how the impact moves their body. If a tire blows out on the highway, the first thing a driver might notice is that the steering wheel feels sluggish. I could even imagine a situation where someone driving sees something unusual up ahead and then smells something dangerous, and turns around in time to avoid driving into an active chemical spill. In that situation seeing alone might not be enough to signal the danger.

I would hope that a competent self-driving car design at least incorporates microphones, and some kind of "body" sensors that would notice an impact, notice changes to balance, and so-on.