Police are, of course, allowed to pull you over if you are breaking a traffic law, such as speeding, driving with a broken taillight, or running a stop sign. They may have a hidden motive for pulling you over, but as long as they have some reasonable legitimate reason for believing you were violating a traffic law, you can be legally pulled over.
Once you are pulled over, police can seize anything that is in plain view. Therefore, if you have marijuana lying in the back seat, or an illegal weapon, the police can take it. If the police have probable cause to believe you’ve committed a crime, they can then arrest you. For example, the police may see an open alcohol container in the back seat and hear you slur your words, and arrest you for driving while intoxicated. Once you’re arrested, the police can perform a thorough search of your entire car and your belongings, and anything they seize can be admitted into evidence against you.
As part of the traffic stop, the police can also make you and your passengers get out of the vehicle. If the police suspect they might be in danger, they can also do a quick pat down. You can also be required to show a valid driver’s license, registration and proof of insurance. If you find yourself in this situation, it is to your best advantage to be cooperative. You don’t have to answer questions the police ask you, however.