OK so your in a different part of the world to me, but what about bidirectional airways.
airway 10 miles wide (rules state that aircraft should be positioned 2 miles form airway edge) leaves 6 miles to play with.
we're allowed to use 3 miles separation between aircraft. if you were one of these aircraft you'd very very quickly have a bad day if the opposite aircraft turned without a word. (even 10deg could cause an awful lot of problems!)
best rule - ALWAYS ASK! can't be said often enough
also most radars today are very good at noticing your path (we use trail dots to give history of where the aircraft has been)