I would suggest implementing a helper
def service_class_helper(route)
classes = ['service']
classes << 'night' if route.night?
classes << 'school' if route.school?
classes
end
and use it in your template accordingly
:class => service_class_helper(route)
If the use of a helper is not desired you can have something like
.service{:class => ['night', 'school'].select { |c| c if route.send("#{c}?") } }
Which does the job quite simple. But is bound to some obvious limitations.