It has been believed that the decrease of the
volume of time used by inhabitants to see their colleges
it still have the similar meaning, if you take out "volume of" and this make your sentence more simple and elegant.
consequence of the existence of
state of the art communication methods
it is too complicated, there are too many "of" there, so it make your sentences hard to understand. Just use "sophisticated ways of communication" if you mean to paraphrase "modern forms of communication".
modern communication equipmentS
such as email and messaging