In general, you have certain protections under the Fourth Amendment which protect you against unlawful search and seizure. This means that an arbitrary search of your vehicle is not legal without your permission or probable cause. That being said, the courts will usually allow law enforcement more leeway regarding searching your vehicle as opposed to searching your home, under the theory you have less expectation of privacy when driving a car and public safety concerns associated with drunk driving or excessive speed. So—an officer can search your car in a DUI arrest if you consent, or if he or she believes there is probable cause to believe there is evidence of a crime inside your vehicle. In the case of a DUI, that “probable cause” could be empty liquor bottles, which would shore up the case against you.
Law enforcement is allowed to search your vehicle if he or she reasonably believes a search is necessary to protect themselves or others. In this case, if the officer believed you had a weapon in your vehicle, then a search could be made without a search warrant. Law enforcement may search your vehicle without a warrant when certain “emergency” circumstances exist—when valuable evidence would otherwise be destroyed before a warrant was obtained. Finally, the police may search your vehicle if it is placed in impound—but may not search a locked compartment in your vehicle without a warrant. As you can see, while you are protected under the Fourth Amendment, there are many, many exceptions which allow police to search your vehicle.
Since many of these exceptions are entirely subjective, your vehicle could certainly be searched without your consent and without a warrant. It is up to law enforcement to determine whether “emergency” circumstances exist, whether it is likely you have a weapon in the vehicle or whether there is evidence of the DUI crime inside the vehicle. Further, if you are arrested for DUI, recent Washington State legislation requires your vehicle will be impounded for a minimum of 12 hours.
