I'd like to object and claim instead that travelling "by" [vehicle] only accounts if you're talking about the means of transportation, but if you're talking about a certain bus, using "by" sounds very odd. ("Travelling by the sixtieth bus"?)
I am wondering if this refer to the route number? Is it bus route sixty-six? If not, how would you say 'We are travelling on bus route 66'.
"A hatvanhatos buszon utazunk."
For numbered vehicles, like bus or tram lines, you use the suffix -as/-es/-ös.
The sentence above refers to the bus that came after sixty-five other buses already departed.
just a small typo: hatvanhatos. Don't ask me why "- os" with hat (6) but the others are as you wrote :)