Hmmm ...: Assuming that "getting away from a tornado funnel that is traveling 10/20/30 MPH" may require having to slug along ultra-slowly in bumper to bumper traffic and since tornadoes move from SW to NE ... why, geometrically, shouldn't one travel 90 degrees to the path line when confronted with bumper to bumper traffic jam speeds??
Hence, it seems like the surest way to put distance between yourself and the funnel's path would be to travel (at whatever traffic speed) in either a NW or SE direction - NOT by slugging along in traffic traveling due south or due north.
Low escapee average traffic speeds as compared to tornado across-ground speeds may modify geometry math.