In Washington state: Where can I legally mount my GPS in my car?

While no WA statute expressly forbids GPS devices in vehicles, the legislature seems to have made clear that the following are not allowed: (1) anything affixed to the windshield that is "nontransparent" that would obstruct the driver's clear view of the highway (RCW 46.37.410); and (2) using either hand to operate a GPS device while driving (RCW 46.61.668). Thus, it seems as though you would be safe by using a voice-operated GPS (because it doesn't require the use of either hand) that is attached/installed somewhere other than your windshield.

I agree in part that you can not obstruct your view of the highway. The statute concerning texting does not state anything about GPS devices. Best practice: don't do anything that will cause an accident. Be safe.