The most common reason for a police stop is a traffic or vehicle-related violation of the law. For instance, police routinely stop vehicles when drivers have violated state traffic laws by failing to properly stop or yield, exceeding speed limits, driving in a reckless or unsafe manner, or following another vehicle too closely. Likewise, police may stop a vehicle for violations of state or local laws related to the vehicle's condition, such as lack of headlights and/or taillights, an excessively loud engine, or impermissibly tinted windows. These police stops typically can result in a verbal warning, a written warning, or a traffic ticket, which may involve a fine and even a court appearance in some circumstances. Police may also stop a vehicle if they have a reasonable suspicion to believe that the driver is violating the law. For instance, if police observe a driver to repeatedly swerve and cross the center line of the road, the police would be justified under the law in stopping the vehicle in order to determine the cause of the swerving, whether as a result of driver distraction, drowsiness, or intoxication.