99% of the answers you got are totally wrong. The spouse does not have any right to use a vehicle they don't own. Neither does anybody else who doesn't have the owner's permission.
We have two vehicles in our house, both legally owned and insured in my wife's name because it was easier that way. I don't have to actually ask my wife for permission every time I drive her vehicles, because we have a very normal marriage and I'm just allowed to drive any time. She even refers to one of the vehicles as "my" car, even though she's the legal owner.
But if my wife were to say (for any reason at all) that I'm not allowed to drive her vehicles, I'm not allowed to drive them. And if I do drive without her consent, I'm guilty of stealing that vehicle. The cold hard written law says driving a vehicle without the owner's consent is theft, and it doesn't matter who the owner is to the driver. It makes no difference whether the owner is a spouse, a family member, a friend or a total stranger.