In Ohio, the answer to this question is “maybe.”
The first thing that should be noted is that for the officer to be found incompetent to testify, he must be out of uniform or in an unmarked car while he is Exclusively or Primarily On Duty for the purpose of enforcing the traffic laws.
In the case of State v. Huth, a sheriff’s deputy worked special duty at an airport. Police officers often supplement their pay by working special duty at bars, construction sites, supermarkets, etc. In fact, many collective bargaining agreements with the police officers’ unions specify how many such hours can be worked and the rate of pay they will make. This officer’s duty required him in part to provide security for the airport by driving on the roads near the airport in a vehicle not meeting the requirements of R.C. 4549.14.
The deputy observed a drunk driving suspect, Ms. Huth, run a stop sign while on a public road and pulled her over. At trial, Ms. Huth argued that the deputy was incompetent to testify because he was driving an unmarked vehicle. But the state of Ohio countered that the deputy was not exclusively on duty for traffic enforcement, but rather to safeguard the airport. Ms. Huth argued back that at the time she was pulled over, the deputy was only concerned with his traffic patrol duties. The case went all the way to the Ohio Supreme Court, which ruled that:
The phrase “on duty exclusively or for the main purpose of enforcing motor vehicle or traffic laws” in R.C. 4549.14 and similar language in Evid. R. 601(C) refer to the officer’s main purpose for his whole period of duty and not to his duty during the apprehension and arrest of the suspect.
Therefore, since the officer was primarily engaged in his duties regarding the safety of the airport, he was competent to testify against Ms. Huth.
