You can reroute avoiding traffic, if the bottom left icon is orange/red then just tap it and you can reroute
It's a manual process but at least you get a visual icon to let you know there is traffic! (And of course a yellow/red overline on the map itself if traffic layer is enabled).
Used the Navigation app properly for the first time yesterday and wondered what the yellow icon was. I thought it was a speed limit warning.
A good tip for quickly adding destinations, from the Google search results on the desktop browser select the 'Places' page and then click the STAR.
In the Navigation app when choosing a destination go to 'Starred Places'. Saves adding anywhere you're likely to visit to your contacts.