has too much detail for you, but would show what are single-deck and
double-deck routes (and usually the length of the bus type), but
currently there are a number of routes in the list that say DD when they
should say SD.

I find to read that listing you do actually need to have some understanding
of bus chassis and body types to know what is single deck and what double
deck. In that listing SD means single door and DD dual door.