You may have already seen this on the news. A tanker full of gasoline crashed in a section of freeway in Oakland appropriately named The Maze. It caught on fire below a freeway overpass. The heat from the fire melted some steel holding up the overpass, which crashed down on the lower freeway section. Two major connectors in the area are now out for at least weeks and possibly months.
Some people are saying this is the worst loss to the local transportation system since the Loma Prieta quake, which is true, and an easy comparison to make since this happened very near to the Bay Bridge and the Cypress Structure, the mile or so of freeway that collapsed back in 1989. But it's also like saying a twisted ankle is the worst injury you have sustained since breaking your leg.
Being a mere mathematician, I have to say that physics has a remarkable ability to surprise. It's surprising that steel can be so fragile, though maybe not that surprising when you think of how much fuel there is to burn in a tanker full of gasoline. It's also surprising that so much weight falling on top of an elevated structure doesn't send the lower level crashing to the ground.
The good news is that no one died in the crash. I doubt that's going to cheer up tens of thousands of commuters today.