You are driving home after a night out. The evening's memories are quickly put to rest by the sight of flashing lights behind you. In a moment, you find yourself responding to the orders of a police officer. You show him your registration, allow him to glance around with his flashlight, even step out. Then he asks that you pop the trunk. You may be wondering if the police officer has the right to ask you to do this and whether you have the right to say no. Well, the answer is: it depends.
The Fourth Amendment Protects Us from Unreasonable Search & Seizure
The Fourth Amendment, as it is generally understood, protects you from unreasonable search and seizure. The Supreme Court has looked at a number of cases involving Fourth Amendment rights and warrantless searches. In most instances, the officer can conduct a search if they have probable cause to do so. This is essentially a hunch backed up by reasonable suspicion. There may be something in your behavior, your physical appearance, or the physical appearance of your vehicle that would prompt an officer to search.
For example, you might have been pulled over because you were driving erratically. However, a smell coming from the car or signs of slowed reflexes on your part may have indicated you are using some type of drug or alcohol. If the officer decided to search your car from glove box to trunk based on the suspicion that you are using and possibly transporting an illegal substance, this would be probable cause.
Search & Seizure of Cars
Other cases involving the search of cars have involved the "plain view" standard and the right of police to search passengers' belongings found in a car. In Chimel v. California, the court held that police may search the person and all areas under a person's control or reach. Anything in "plain view" can be seized. This standard includes car searches. In Wyoming v. Houghton (1999), the court ruled that if the officer has probable cause to search the car, they can also inspect passengers' belongings. The idea is that the item, a purse for example, might conceal the object of an officer's search.
Search & Seizure of the Trunk of a Car
The same reasoning can be applied in the case of a trunk. It would be in control of the car's driver, and barring some unusual circumstance, within his or her reach. A trunk generally conceals its contents. So, an officer may look there if there is a belief that what he is searching for might be in the trunk.
No Warrant is Required to Search a Car
Another point on law enforcement's side is that cars are generally excepted from the advance warrant requirement because of their mobile nature. This gives them license to conduct warrantless searches of cars. An officer only has to meet the probable cause standard in most instances. This is relatively easy to do. Proving that an officer did not have probable cause is much more difficult and has only succeeded in a few cases. Most of those cases have involved racial profiling of some type, lack of consent, or a small exception in the public's favor...traffic violations.
The Supreme Court ruled in Knowles v. Iowa that police cannot search a driver or passengers after ticketing them for routine traffic violations. In its decision, the Court said that a traffic violation is not an "arrest." Police officers' ability to conduct searches is limited so you would not be in their custody. The probable cause argument is also diluted in this case. Ticketing you for turning right at a red light does not give an officer probable cause to search you or your car. Traffic violations are not inherently connected to any other criminal activity. This voids a claim of "reasonable suspicion" on the officer's part.
This was a small win on the part of individual rights. Interestingly, Fourth Amendment questions are frequently part of the court's docket and more exceptions may be coming. In the mean time, it is probably best not to carry anything in your trunk you wouldn't want a police officer to see.