Can you double clutch downshift a big rig if your brakes are out? I mean your revs are already up going downhill trying to compression brake and your thinking "let me push in the clutch to lose any compression braking and try and find a lower gear..."?
No, not to get into 3rd or 4th, once momentum creeps up and you don't have brakes to slow down, it pretty much ain't happening. You start the grade in a lower gear, jake brake on and do not up shift, truck picks up speed, on the brakes hard enough to slow back down and off the brake, once they heat up you are done. I had a driver pass me going down a mountain pass in West Virginia one time, he had been on the brake so much and so hard the trailer brakes were on fire.....literally, one in PA too..
Just a few points on the driver: Young (20 I believe) inexperienced unseasoned driver..........Could not read, speak or understand English so I'm not sure if he even knew what a runaway ramp was for. He had to have a translator for the trial........Castellano Trucking had a DOT write up sheet a mile long, including two OOS violations very recently, I quite reading it at over 30 violations in the last few months.....The trucking company has dissolved since the accident, probably anticipating lawsuits. He was here on a green card and had a valid Texas issued CDL, not that that matters, but he should have been trained more thoroughly though.
Bottom line, the trucking industry is so desperate for drivers lots of people that have no business behind the wheel of an 18 are in fact driving all over the country. You put an inexperienced driver in front of 40 tons and expect them to be successful guiding that 40 tons down a 7 or 8 percent grade from 10,000 feet in elevation is a nail biter. Can some do it, sure, but some cannot.
I have had young drivers at warehouses come up to my truck and ask me if I could back theirs into the dock, no lie, more than once. I said nope, but I'll be glad to guide you as long as you watch me and listen.
There are a few companies out there that will team you with a seasoned driver for a few weeks before going at it alone, they probably have pretty good success with that.