You have to factor in startle factor, panic, etc. I had ChatGPT model it.
Because the truck had to
slow and set up for the U-turn, an attentive driver could plausibly notice the developing hazard
before the trailer fully blocked the lane. That increases DD compared with a pure “instant wall” scenario. U.S. highway design guidance assumes
~2.5 s perception-reaction time at
70 mph, which produces a recommended
stopping sight distance ≈ 730 ft—a good benchmark for when a prudent driver would start braking the moment a maneuver looks wrong.
Texas Department of Transportation
Below is the
allowable reaction time at several plausible “first-notice” distances DD. (Same minivan, dry pavement, straight road.)
| First notice distance DD | Max reaction time to still stop |
|---|
| 300 ft (you notice late, as the trailer starts blocking) | ~1.09 s |
| 400 ft | ~2.07 s |
| 500 ft | ~3.04 s |
| 600 ft | ~4.01 s |
| 730 ft (AASHTO SSD @ 70 mph) | ~5.28 s |
| 800 ft | ~5.96 s |
So,
if you were truly paying attention and began braking as soon as the truck’s maneuver became clearly hazardous (say D≈500 − 730D≈500−730 ft), the
needed reaction time to stop safely would be roughly
3 to 5¼ seconds. That’s far longer than typical human perception-reaction times (~1–2 s) and therefore
feasible,
but only if you start braking the instant the U-turn looks wrong—not after the trailer has already swept into and blocked your lane.
Two important takeaways:
- Once the trailer actually blocked the lane and the available distance collapsed to <~200–300 ft, a safe stop became physically impossible (braking distance alone at 70 mph is ~188 ft).
- Highway design’s 730-ft stopping-sight benchmark (built using 2.5 s reaction + conservative decel) shows how much distance you typically need at 70 mph for a comfortable, defensible stop—useful context for juries and recon reports.
None of this takes into account mechanical failures, either. Let's suppose the brakes failed, the tires were old, etc. They had no chance. It's easy to second guess someone in the final seconds of their life, but when adrenaline hits, all bets are off.
