“This recommendation would essentially make navigation unusable. The system could still give an auditory warning for the next turn, but without being able to glance down at the map and see how close the next street is would likely lead to a lot of missed turns and resultant frustration. And although NHTSA includes the results of driver distraction studies in the guidelines, it has no testing directly related to using a navigation system. Instead there are more general conclusions against any tasks that require looking at a device for periods of more than 2 seconds, or a series of glances that amount to more than 12 seconds at at time.
I would think that looking at a static map, and trying to find the particular street which you are on, would by much more time-consuming than seeing your exact position on a dynamic map.”
via Instapundit.