If the map and road sign disagree, just do what everyone around you is doing (ie, go with the flow) until you recover agreement. It's not perfect, but stretches out attacks to having to compromise long stretches of road and multiple vehicle types. If the cars for the next mile somewhere can find pace, the whole group can; similarly, if any kind of car can find pace, they can all use that to set.
Obviously safety checks and such, but human drivers only loosely follow signs and often get behavioral cues from other cars -- why can't automated cars do the same when they get confused?