If there's road construction ahead, the friendliest alert is a warning: Heavy traffic, take an alternate route.
I can take this information and action it, or I can take it as advice and override it. Because I need to go to a store along the way. Or I live along the road but before the area I know the traffic is. Or I'm just feeling lucky, besides those signs are sometimes wrong and Waze is showing it's fine.
If, on the other hand, there's a giant chasm in the road ahead, the friendliest alert is a big sign saying DO NOT ENTER.
I can take this information and action it, or I can keep driving and fall into a giant chasm like the old Saturday Night Live skits with the driving cat.
Sometimes when designing an interface, we're hesitant to throw an error. It doesn't strike us as user-friendly. Sometimes, though, when the road is out? A big DO NOT ENTER sign is the friendliest thing to do.