what he said plus....
As long as its not attached to you and concealed. Unloaded... you can velcro it to your forehead and drive with the mag or speed loader in your hand (although not recommended).
RCW 9.41.050
(3)(a) A person at least eighteen years of age who is in possession of an unloaded pistol shall not leave the unloaded pistol in a vehicle unless the unloaded pistol is locked within the vehicle and concealed from view from outside the vehicle.
Code of Federal Regulations
Title 18 - Part I - Chapter 44 - § 926a
§ 926A. Interstate Transportation of Firearms
Release date: 2005-08-03
Notwithstanding any other provision of any law or any rule or regulation of a State or any political subdivision thereof, any person who is not otherwise prohibited by this chapter from transporting, shipping, or receiving a firearm shall be entitled to transport a firearm for any lawful purpose from any place where he may lawfully possess and carry such firearm to any other place where he may lawfully possess and carry such firearm if, during such transportation the firearm is unloaded, and neither the firearm nor any ammunition being transported is readily accessible or is directly accessible from the passenger compartment of such transporting vehicle: Provided, That in the case of a vehicle without a compartment separate from the driver’s compartment the firearm or ammunition shall be contained in a locked container other than the glove compartment or console.