"Brake, brake, BRAKE!
I can't brake 'cause it's already broken!
Oh, my God, we're gonna crash!
(screaming) ... (crash)" ~ The crash on SSS Centerprice...
In The First Encounter, The crates make their first appearance as secret, but only as a Crate Car and a Crate Pyramid, while in The Second Encounter they take flight to follow Sam to Sirius. When Sam's Spaceship goes much faster and they can't catch up, they decided to use Hypercrate to speed up the Crate Bus but when they nearly gonna collide with Sam's spaceship the brake to the Crate Bus broken thus it crashed impact onto Sam's spaceship. Also, take note that Sam hates crates...probably for making him crash on Earth, stopping him from reaching Sirius and killing Mental. Maybe Mental's minions broke the brakes on the Crate Bus to stop Sam from reaching him or the brake really is broken? Nobody will ever know...
A Crate Bus has a total of 24 seats, 12 on each side (duh), it also seems to have two parts. The first part has 7 seats on one side and the other one 5.