A driver can stare straight at a parked truck and not see it in time. That is not always inattention. Often it is how the eye and the brain are built.
The illusion of slow
Speed is not something the brain measures in absolute terms. It reads it off relative motion, the world sliding past. On an open highway everyone around you moves at nearly the same velocity, so the flow across your eyes goes quiet, and the nervous system concludes you are barely moving, even at seventy, where you are covering about 103 feet every second. The feeling of going slow is real. The physics underneath it is not.
The object that breaks the spell
A stopped car or a slowing rig produces almost no looming, the swelling of an object on the retina that the brain uses to feel an approaching collision. Against a stationary object that cue builds slowly and then explodes in the final moment, which is exactly when there is no road left. Add pre-dawn light and a lane the driver is not scanning, and a competent person can look right at a wall of steel and not register it as one until it is too late.
The second and a half
Even an alert driver needs time to perceive a hazard, decide, and move a foot to the brake. Traffic engineers design for a perception-reaction time of about 2.5 seconds. At seventy, a second and a half is more than 150 feet gone before the brake light ever comes on, often more distance than the driver ever had.
The lesson
The defense reaches for "he just was not paying attention." The truer and more provable story is usually a stopped object in a live lane, poor conspicuity, dim light, and a normal human perception budget the hazard swallowed. You prove it with the download, when did braking actually start, with the lighting and reflective markings, and with the timeline of why something was sitting still in a travel lane. Looking is not seeing, and the difference is measured in feet the driver never had.
On perception-reaction time as a design value, see the FHWA Speed Concepts guide. This is general information, not medical or legal advice.
