A compound sentance has two independant clauses, meaning it could turn into two different sentances. A complex sentance has a dependant clause and an independant clause.
So let's take the first clause. "We had been on the road for six hours," that can be a sentance by itself, so that is one independant clause. The second clause "it felt like sixty given the appaling surface," is also independant. Therefore, it is compoud. Keep in mind that the "but" doesn't need to be considered as muc because in a compound sentance conjunctions are often used to link the two clauses together.
Hope this helped! - Blue Jay