Just looking at the hill they were going down, it stretches for a couple of miles. You would have to be on the brakes the entire way down, and if the brakes fail, there is absolutely no hope of stopping.
Steep hill, car with weight like this would have easily picked up speed in excess of 60mph. Only two things here, unfamiliar driver missed stop sign on bright afternoon day (maybe distracted?) Or total and complete catastrophic brake failure.
“there is absolutely no hope of stopping.”
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Some roads in that area have an uphill pull-off ramp to handle break failure before careening to the bottom.
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The other thing to do in a vehicle like that, one most people don’t do, is to downshift to a lower gear on a hill where the breaks would take too much wear, like second or third in that vehicle. IIRC I had a 2000 Navigator, a vehicle much like the Excursion, but shorter, and it had a 4 speed transmission.