It is important, when interpreting eyewitness accounts, to keep track and acknowledge the kinds of perceptual and memory mistakes that people tend to make without losing the value of the actual report. I'm sure that a little exertion can produce a simple mundane explanation that fits the facts better than a kangaroo does.
Because our own experience colors our readings, I connect this report to my own experience of sleep deprivation back in 1980. I was riding shotgun at night in the long, empty expanses of West Texas, and I began to see tall men in hats running across the road and vanishing in the crossed beams of the headlights. I had been up for over 24 hours and the men had a pixellated appearance, as if they were part of a more sophisticated videogame than was available at the time, so I could tell they were hallucinations; also, they did this repeatedly and the driver could not see them, so this doesn't fit the facts much better than the kangaroo, except for the "man running across the road" element.
Since you both saw it, it was either a mobile object or conditions were such as to subject both of you to the same optical illusion. Since it has such a similarity to my man-in-the-crossed-headlights vision, I wonder what there might be about empty roads, headlights, and nighttime that might combine into running man illusions.
I'd also ask around for stories about that stretch of road. Stories don't prove anything (many ghost stories are explanatory fables for misunderstood phenomena), but they make everything more interesting.