What would you have done?

The other day, I was driving westbound on I-94, a few miles east of Barker Road. It was late in the afternoon, toward the end of rush hour, so traffic was a bit heavy and slow moving. As traffic began to break up a bit, I noticed that the car ahead of me kept swerving out of his lane. (We were in the middle lane, so there was one lane on each side of us for him to veer into.)

It was obvious that this driver was somehow impaired and that he only had partial control of his vehicle. Through his back windshield, I could see the driver vigorously shaking his head back and forth. He was either trying to wake himself up, or sober up. Was he a drunk driver? Or just a guy who desperately needed a nap? Either way, it seemed like a dangerous situation.

As I followed behind at a safe distance, my heart rate began to speed up. It was one of those scenarios where you are just waiting for something bad to happen. Just as I was about to get on my cell phone to call 9-1-1, this driver took the next exit, and was soon gone from my sight. Hopefully he headed straight for a hotel, or a gas station to purchase an energy drink. The sooner he got off the road, the better.

If I would have witnessed his car sideswiping another driver, I would have felt terrible for not being proactive in reporting the situation. But what is the best course of action in a situation like this? Is it appropriate to dial 9-1-1 to alert the local authorities? Is it feasible to expect the cops to locate this driver in a timely manner?

If you had witnessed this driver swerving in and out of his lane, what would you have done?