Because crash tests measure outcomes of passengers, not of the car itself. And even the safest vehicles usually fare poorly when the other vehicle is way heavier.

No amount of engineering can change the basics of physics. A firetruck has a roll weight of in the ballpark of 50,000 lbs. A Tesla has the ballpark weight of 4,000 lbs.

You need a lot of V to make up for that difference in M.

On top of that, a firetruck is typically built on really tough commercial chassis which has a feature a lot of rigidity.

It's worth separating the momentum M*V you're referring to, from the energy M*V^2 that's dissipated in deformation in the collision.

Hmm I'm not quite satisfied even by my clarification. Car and truck chassis strength needs to scale with something closer to M*V^2, so the truck chassis is multiple times stronger.

Somewhat related fascinating take: A schoolbus driver did a tiktok saying, roughtly: For its size, a schoolbus is a relatively lightweight vehicle. We don't have Mansfield Bars because we don't want to absorb the impact of you running into the back of us and pushing us into children. Instead, you go underneath and the children have a better chance of surviving. Pretty sobering.

Losing to a fire truck is hardly an indictment against a car's safety. Everything loses to a fire truck.

I don't know about Teslas, but with cars in general, getting good scores on crash tests means that the people in the car are more likely to live. One way this is accomplished is by letting the car absorb more of the kinetic energy (using crumple zones, etc), so the cars themselves end up coming out of it much worse.

Aren't interstate roads highways in the US? I don't think it matters what your safety score is if you crash into a stationary object at 100-120 km/h, the car obviously gets destroyed.

I suspect the tesla went under the truck in this case, chopping the top off. I doubt other passenger cars would have done better :/

From the video in the linked page, it doesn't look like it went under. The B and C pillars are largely intact, as is the roof between them. The front end up to the A pillar is gone, and the space between A and B pillars is pretty squished.

A fire truck is a 30-ton hunk of metal. That mass disparity really does make a huge difference in collisions. Pretty much any sedan-sized vehicle is going to be obliterated in such a collision, regardless of crash test scores.