I forgot to link the collision test video. Here is a video for the Variocage, the only crash tested dog crate which is also only sold in the UK. The people that sell the Variocage also sell car harness that have been crash tested.
I think I have found a crash tested car safety harness sold in the US after all. It looks like you have to find a local dealer that carries it though. I don't see a way to order it directly from their website.
Here is the harness on their website:
-