Routine traffic stop is a phrase used to describe a common vehicle code violation. In reality, there is no actual "routine traffic stop law." A law enforcement officer, pursuant to a driver committing a violation of the state or local vehicle/traffic code, initiates a traffic stop.
Routine Traffic Stop
A routine traffic stop always begins with a law enforcement officer witnessing a violation of state or local vehicle code law. Generally, the officer will check the car's license plate number to determine if the car is registered or whether it is stolen. The officer may decide to issue a citation or warning for the violation and then release the driver.
An example of a vehicle code violation that is fairly common and warrants a traffic stop is California Vehicle Code Section 21461 (a): "It is unlawful for a driver of a vehicle to fail to obey a sign or signal defined as regulatory in the federal Manual on Uniform Traffic Control Devices, or a Department of Transportation approved supplement to that manual of a regulatory nature erected..."
An example of this would be failing to stop at a "STOP" sign.
An example of a not-so routine traffic stop is one where the car has been reported stolen. The level of danger associated with these type of stops is exponentially greater and officers must prepare to confront a threat.