Here's what we do know:
* Fossil evidence: Fossil discoveries of Brachiosaurus are rare and usually individual bones or incomplete skeletons. This makes it hard to study herd behavior from fossils.
* Comparisons to other dinosaurs: Some scientists speculate that Brachiosaurus may have traveled in small herds, similar to modern giraffes. This is based on the fact that giraffes are the closest living relative to Brachiosaurus in terms of size and feeding habits.
* Possible reasons for herds: Herds would have provided protection from predators, helped with finding food, and possibly facilitated mating.
In summary: While we can't know for certain, it's likely that Brachiosaurus traveled in herds, but the size and composition of these herds remain a mystery.