Random witnesses can not give such testimony because they are not qualified. All they can testify to is what they saw. They would not be allowed to enter testimony about who is at fault unless, by some miraculous chance, they happen to be experts in that field.
If the intersection was obstructed as you say, then why did Jack enter it without being aware of the approaching vehicle? The exact wording of laws varies, but all the ones I am aware of say that, at a stop sign, you must come to a complete stop, ensure that there is no approaching traffic, and only then may you proceed. Simply stopping does not allow you to immediately proceed. If the view of the intersection was obstructed then why did Jack drive into it? And if he carefully nosed out into the intersection to check for incoming traffic, then how did he manage to get hit? At worst Bob could only have clipped his nose, and even then only if he made no effort at all to swerve even a few feet. Is that the case? If so then it changes the case completely, and most of the fault now rests with whoever maintains the road, with neither driver bearing more than a tiny fraction of responsibility.
Almost certainly not.
Driving drunk slows your reaction time and diminishes your perception. That is well established in both science and law. Even absent any testimony this is evidence that Jack might have avoided the accident had he not been drunk.
The problem is that traffic accidents are almost never unavoidable, and the courts are aware of this. I have lost count of the number of times that I have indisputably avoided accidents that other people would have caused, including scenarios almost identical to the one posed in the OP.
The accident as described was not unavoidable. Since Jack had stopped, he should have had a clear view of the intersection before he proceeded. Failing to do so is itself a violation of traffic laws over most of the planet. You simply can not drive into a blind intersection. If the entire intersection actually was obscured by shrubbery then whoever is in charge of the road is at fault, but I have never actually seen an intersection where you can not gain a clear view of the intersection by just edging out over the line by a couple of feet. I can’t even imagine how that could be. Even on roads with solid walls built up to channeling, you can still creep out a little and have a look before driving into the intersection.
The claim that Jack never even had awareness of Bob’s vehicle before he was hit is itself evidence that Jack was being inattentive and driving unsafely. If he says that in court, then it will immediately become plausible evidence that his driving was affected by alcohol. And if he lies and says that he did see Bob coming, but thought that Bob was going to stop, then it will be argued that his inability to judge speeds was due to his inebriation.
And this is why, regardless of testimony, Jack will almost certainly be found to be partially at fault. Alcohol impairs judgement, perception and reaction times. No matter what testimony is given it is going to be difficult to convince the judge/jury that Jack absolutely, 100% could not have avoided the accident if he had been sober.
And I agree completely with that concept. About the only accidents that are completely unavoidable are the ones where another car swerves from their lane into yours. With almost any other accident, a skilled driver can take steps that reduces the chance of the accident occurring. I’m not saying that they will always be successful, but the chance exists and being drunk diminishes that chance greatly.
Sure, Bob shares much of the blame, but it’s more than plausible that if Jack hadn’t been drunk then the accident would never have occurred. Road safety depends on the cooperation of all road users. Bob should not have to bear full responsibility for a moment’s inattention when the accident could have been avoided completely if Jack had not spent an hour drinking and several more minutes driving while drunk. Jack’s contribution to the accident was deliberate and prolonged and he had numerous opportunities to avoid it. Bob’s contribution was the result of milliseconds of inattention.
And that is very likely the way any court will find and certainly the argument that will be pursued by anyone with a financial stake in the case, especially insurance companies.