The Brunette team rides in the bottom of the bus.
The Blonde team rides on the top level.
The Brunette team down below is having a great time, when one of them realizes she doesn't hear anything from the Blondes upstairs. She decides to go up and investigate. When the Brunette reaches the top, she finds all the Blondes frozen in fear, staring straight ahead at the road, and clutching the seats in front of them with white knuckles.
She says, "What the heck's goin' on up here? We're havin' a grand time downstairs!"
One of the Blondes looks up and says, "Yeah, but you've got a driver!"