Eyes wide shut: distraction having the eyes on the road

Since the 100-car study, it has been generally recognized that a driver, having the eyes-off-the-road for 2 seconds or more is unacceptable in terms of traffic safety. Since driving is primarily a visual task, having no relevant driving information fall on the driver’s retina is a safety factor with high face validity since it disables a driver to respond to visual cues of running off the road or a lead vehicle braking. However, the opposite is not true either: A driver having his eyes on the road does not mean that all relevant information falling on the retina will actually be processed. In this process, selection and attention play an important role. What safety consequences does it have when a driver is looking outside, but is focussing on distracting elements along the side of the road (e.g. billboards), or maybe even looking on the road but not paying much attention to the driving task. What sort of risk do we run when we are daydreaming, talking on the phone, looking at our HUD or looking for 2 seconds to a billboard that still allows us to see the onset of braking lights of or lead vehicle?