YABU. My DH was rear ended in stop start traffic on a motorway (less than 10mph though). He was driving my small car and other driver had a fully loaded transit. The mass of the vehicles has a big impact on damage, as well as the speed. Basic physics, innit?
My poor car was written off, even though it just looked like scratches on the outside. Had to buy a new car, cost us an extra £1600 that we weren't expecting to have to spend at the time (was planning to replace car in around 15 months and was going to use that time to save). Also saw our insurance premiums go up because the guy's insurance company disputed fault for 9 months (even though it was obviously his fault and he apologised and took blame at the scene). During that period, we had to renew my husband's insurance on our other car. Premium was £150 higher as we had an unresolved claim. Was settled 6 months later after they finally admitted fault. But our insurance company only refunded the higher charge on a pro rata basis.
We were also sent threatening letters by the other insurance company saying we had to use their people for hire cars etc to minimise the loss. Except they sent that 2 weeks after the accident and refused to engage with my insurance company before that. So we had to use a different company to provide a hire car (I had to get to work!) and his insurance company threatened us again and said they wouldn't pay. They did eventually, but only after a number of letters and hours spent sorting it out on my part.
So essentially my husband did nothing wrong, he was driving at a sensible distance and stopped in plenty of time as did the rest of the drivers stuck in stop start traffic that day. The transit driver wasn't paying attention and hit my husband. It caused us almost a year of hassle, hours and hours lost to sorting it all out, hundreds of pounds in increased insurance costs, and we had to borrow to buy a new car much earlier than expected instead of being able to save up and pay in our own time as we had planned.
And that was a minor accident with no injuries; my husband had mild neck pain which he took ibuprofen for and didn't claim anything.
Your 'hubby' is being VU. Drive properly and safely, pay attention, especially if driving a truck FFS. I hope he's now going to admit fault immediately and make sure his insurance company is behaving properly.