The first time I crossed the path of the May 20, 2013 Moore tornado at night I was really taken aback. Both sides of I-35 the entire way through Moore are normally lined with shops, strip malls, entertainment venues, and hotels, and are normally all lit up at night. The tornado, however, wiped out everything in its path, leaving a rather large and noticeable gap in the lit area.
I shot the video below crossing the path of the tornado on I-35 going northbound from Norman towards Oklahoma City at night. The video starts at the S 19th St exit, crosses the tornado path where the medical center once stood (which will be on the left), and ends at the S 4th St overpass. You will notice that both sides of the highway all of a sudden get very dark. That is the tornado path you are seeing.