The Twelfth Doctor told his TARDIS that it was a vehicle. (TV: The Husbands of River Song) Missy once told Clara Oswald that one should "never believe a man about a vehicle". (TV: The Magician's Apprentice)
Following the Thal-Dalek battle, the Thals had developed vehicles for themselves. As they were based on the drive principles of the Dalek War Machines however, these vehicles needed a constant feed of static electricity to function, only being operable within the Thal City. (AUDIO: Return to Skaro)