¶45 Another factor weighs strongly against the reasonableness of the protective search in this case. Before Johnson was asked to exit the vehicle and submit to a pat down, he gave Stillman paperwork showing that his vehicle had passed an emissions test recently, and that, as a result, the registration suspension had been lifted. Officers may detain a person on a stop for a routine traffic violation only for as long as necessary to complete the investigation of the violation. See Knowles v. Iowa, 525 U.S. 113, 117 (1998). The paperwork Johnson provided to Stillman established that Johnson’s vehicle was no longer subject to an emissions suspension. 
 We recognize that the officers noted that Johnson had failed to signal a turn prior to the stop. The record does not establish whether the officers had finished their investigation with respect to his failure to signal a turn. What is clear in light of Knowles v. Iowa, 525 U.S. 113 (1998), is that once an investigation for a minor traffic violation is completed, the officers’ generalized concern for safety does not provide a basis for a full protective search.