Circumferential cracking in the asphalt is the only way to identify these. But, if one is descending fast, it's almost impossible to notice these cracks.
Metering Mode: center weight Exposure time: 0.013 s (1/80) Aperture: f/4.5 Focal length: 18.3mm (35mm equivalent: 93mm) Flash: No File size: 2289419 bytes
Closeup of "invisible" sinkhole on Mt. Umunhum Rd. (1900ft)