Preferred Roads would allow a user to specify a list of roads they are more familiar with and prefer to take where possible, whether manually, or automatically through repetitive driving habits.

If a new route might save me 2 mins I don't care. I would still prefer to use my most familiar roads. If there is an accident and I should avoid to save 10 mins, then it could utilize less familiar roads.

Along the same lines, another collection of roads could be considered roads to avoid. This is different to avoiding Toll roads, as some toll roads are preferable over others. This can allow Waze to quickly prioritise familiar roads and avoid roads they know cause issues other than heavy traffic or long delays.

The threshold of choosing a non-preferred road could be a percentage of the calculated journey times. If it will save me 5 mins and I'll be driving for an hour, big deal. If it'll save me 5 mins and I'll be driving for 10 mins, that becomes more worth while, and the non-preferred roads may then be taken.

Using an algorithm here means we can escape having a warning every time, but showing an icon to allow us to decide before our drive would still be valuable.