The less the danger, the fewer people are waiting in line for the roller coaster.
Fewer [THINK: Formal count]
Less [THINK: Lower the mass]
“According to usage rules, fewer is only to be used when discussing countable things, while less is used for singular mass nouns.
“…fewer ingredients, dollars, people, or puppies…less salt, money, honesty, or love.”
“If you can count it, go for fewer. If you can’t, opt for less.“
[read more about it on blog.dictionary.com]