Grammar Question involving "when"?

It seems to me that your problem isn't with "when" but how could you have them/him drive when he was already driving? Obviously, only Rick was behind the wheel, but all were in the car so all were driving -- as opposed to flying, swimming, or sailing. In English, as in your sentence, all people in a car can be driving, not just the driver. Non-drivers can be "riding" but look how cumbersome that sentence would be. It could be said with different verbs: R, M, & S were traveling to ... when R fell asleep and drove.... - or R, M, & S were driving ... when R fell asleep and steered off the road, or the car drove/drifted off the road. It could be said many ways, but, basically, "to drive" has several meanings and two are used in the sentence.

Each of these has two meanings of "to drive:"

I was driving (traveling, going) to New York when I drove (steered, turned, exited) into the rest area.

I was driving (traveling) in the right lane (or just "was in the right lane") when I drove (steered, turned) onto the exit ramp.

I was driving (traveling, moving, positioned) in the left lane when I accidentally drove (grazed, scraped, drifted) into the guard rail.

Rick drove the car off the road when he fell asleep at the wheel.

That's the correct anwser.

Sorry, I just don't understand the construction of the question. The answer solves the problem as to who was driving, but it wasn't included as one of the alternatives in brackets - nor was the bit about driving off the road. Anyway, if you stick the answer after the word Chicago, it reads pretty smoothly to me.