Plotting a course on Google Maps, I think this would add ~1.4 mi if you go around to get to the other side from where they were.

The fire station was located on the opposite side of runway 4 from the United plane. To avoid crossing the runway would mean having to travel a few extra miles around the thresholds (I assume).

I guess they could have found a route that wouldn't conflict with landing aircraft, but I doubt that's a practical option most of the time.