Mix standard and gravel routes

Hi everyone, just started using cycle.travel and I’m blown away, as a web developer nerd myself it’s amazing what you have built. 

I’m also an avid gravel biker / tourer and I enjoy routes with a bit of everything apart from busy roads! What’s everyone’s approach to mixing standard and gravel routes to make a hybrid route? I enjoy a nice 50 / 50 road / gravel with maybe a slither of single track.