When transporting your firearm in a vehicle, it must be unloaded, with neither the firearm nor any ammunition readily accessible or directly accessible from the passenger compartment of the transporting vehicle. If the vehicle does not have a compartment separate from the driver's compartment, the firearm or ammunition must be unloaded and contained in a locked container other than the glove compartment or console. If you are transporting your firearm in a manner other than in a vehicle, it must be unloaded, inside a locked container, and separate from any ammunition.
As an exception to the requirement above, if you have a DC concealed carry license, you may lawfully transport your registered handgun concealed on your person while in a vehicle.
Reference: DC Code § 22-4504.02.