The Influence of Officer Positioning on Movement During a

Threatening Traffic Stop Scenario


William J. Lewinski, PhD, Force Science® Institute

Jennifer L. Dysterheft, Graduate Student, Minnesota State University, Mankato

Dawn A. Seefeldt, MA, Force Science® Institute

Robert W. Pettitt, PhD, Minnesota State University, Mankato


Law Enforcement Executive Forum  March 2013


Conducting traffic stops is a routine patrol duty of police officers. The most frequent and visible interactions between police officers and the public take place in motor vehicles, most commonly at roadside traffic stops (Eith & Durose, 2011; Harris, 1989; Pinizzotto, Davis, & Miller, 2008). Officers successfully complete the majority of “routine” traffic stops without facing the threat of injury; however, traffic stops can place officers at risk of injury or death either by intended or unintended actions by an assailant or others (Payton, 1964). According to the California Commission on Peace Offi- cer Standards and Training (2005), traffic stops “can be one of the most dangerous duties a patrol officer can perform” (p. 1-3). In a study investigating officer attacks while performing routine traffic stops, one officer reported that as he approached the back door of the vehicle and informed the driver he was stopped for speeding, the driver’s only response was “two shots in the chest from a handgun . . . into my vest” (Pinizzotto et al., 2008). From 2001 to 2010, approximately 60 of 541 officers who were feloniously murdered in the line of duty were killed during a traffic stop, and 55,000 were injured during a traffic stop or pursuit (Federal Bureau of Investigation [FBI], 2010; U.S. Department of Justice, 2011).


Although many departments have added various adaptations to traffic stops, these tac- tics, created by some of the best tactical officers in the United States, were not developed from scientific research. As noted by Justice Scalia, there is a paucity of research on officer safety in relation to the dangerousness of traffic stops (Maryland v. Wilson, 1997). This article is an effort to form discussion on the current research involving officer traffic stop procedures.


One of the more common training procedures is the position an officer takes in relation to the vehicle. Officers are often instructed to stand on the passenger or driver’s side and at some distance or angle to the B-Pillar of the automobile (Adams, McTernan, & Remsberg, 2009; Payton & Amaral, 1996; Perry, 1998; Remsberg, 2003). The B-Pillar is the second pillar from the front of the vehicle in the pas- senger compartment and is located just past the seat or in alignment with the front passenger seat. Historically, officers have assumed positions at the B-Pillar that are in front of or behind the pillar and at the classical angles of 45o, 90o, and 180o. For example, an officer can stand at the driver’s door with his or her right leg close to the B-Pillar and his or her body in front of the pillar at a 45o angle align- ment with the vehicle. This places the officer at an opportune position to view inside the front passenger compartment of the vehicle as well as offers time to react if the driver were to pull a weapon (Adams et al., 2009; Perry, 1998; Remsberg, 2003).


In addition to B-Pillar alignment, officers are taught to consider the “threat zones” of vehicles when performing traffic stops. As defined by Remsberg (2001), these threat zones are areas relative to an offender’s vehicle in which officers are vulnerable to an attack. For the present study, Remsberg’s “crisis zone” was used to determine the Mitigation Zone (MZ) for the driver’s side of the vehicle. The “crisis zone” or MZ is an area where the officer is at a position of reduced risk because the configuration of the vehicle being stopped impairs or restricts the driver’s visual access or weapon alignment on the officer. The MZ on the driver’s side is defined by a 10o angle, extending outward from the B-Pillar and facing the rear of the vehicle.


As addressed by Remsberg (2001), the more an officer is caught offguard, the larger their startle response will be and, consequently, it will take them longer to react. Reaction time is the length of time it takes to perceive a stimulus and prepare a response, whereas movement time is the duration of time it takes to complete the response (Remsberg, 2001; Vickers, 2007). Kinesthetic reaction time occurs faster than auditory or visual reaction time at 0.12 to 0.14 seconds (s) (Vickers, 2007). This human startle response, or kinesthetic reaction, is a person’s physical response to a sudden, intense stimulus (Davis, 1984). Most often, a startle response will cause a person to experience a series of muscular contractions taking place within milliseconds of the onset of the stimulus and may end just as quickly. Common responses of the body are fist clenching or hand grasping, occasional teeth baring, forward movement of the shoulders, bending at the hips, and so on (Davis, 1984). In relation to possible officer response reactions, according to Jones and Kennedy (1951), the sound of a pistol shot can induce a startle response in the trapezius muscle, causing a shrugging motion, within 25 to 50 ms (Davis, 1984). These responses were often completed within 0.2 to 0.5 s (Jones & Kennedy, 1951). In addition to muscular contractions, this startle response evokes an elevation of heart rate, although this varies considerably among different individuals (Eves & Gruzelier, 1984). As officers often anticipate risk or prepare themselves for action when performing traffic stops, similar to athletes preparing for competition, officers’ heart rates may increase as much as 25 beats per minute (bpm) prior to even performing a task (Sime, 1985). Overall, reaction time, startle responses, and choice of tactical movement may assist in playing a detrimental role in the amount of time officers take to respond to a deadly threat and reach a safe zone.



The primary purpose of this study was to assess the various positions officers take after walking up to a vehicle while conducting a traffic stop and to evaluate whether those positions inherently have some element of safety that an officer can rely upon, before, during or after an assault. A secondary purpose of this study was to observe the automatic reactions, tactical responses, and movements made by the officers. In particular, reaction and movement times were measured in relation to threat presentation. Because the body can begin to process and react to information faster than the eyes and ears, officers’ startle responses to the presented threat were also observed for study purposes. When observing officers in the following traffic stop scenario, the goal was to investigate the types of startle responses they had during retreat, in addition to how these responses influenced their reactions and movement speed. Prior to this study, there had been no formal assessment of officer reactions in a threatening traffic stop scenario.






An original sample of 94 participants from police agencies from the states of Oregon and Washington volunteered for the study. Of the 94 participants, one was eliminated from data analysis due to equipment malfunction during the experimental trial, resulting in a total sample of 93 participants (13 females and 80 males). The sample included the following rankings: one Captain, two Corporals, three Deputies, two Deputy Sheriffs, 10 Detectives, 68 Officers, one School Reserve Officer, four Sergeants, and three Senior Reserve Officers. The participants’ experience in law enforcement was 12.4 ± 7.4 years. All participants were told that the primary purpose of this research project was to “better understand officer movement in response to a threatening traffic stop.” Participants were not informed of any specifics of the study until meeting with an investigator in the warehouse. All participants completed informed consent waivers before entering the warehouse.


Participants also completed a health screening and fitness level questionnaire (range 0 to 10) (George, Stone, & Burkett, 1997). The participants’ demographics were as follows: age = 38.8 ± 7.3 years; body mass index = 28.9 ± 4.23 kg/m2; maximum oxygen uptake (VO2max) = 38.59 ± 7.04 ml/kg/min, where VO2max was estimated using the regression equation by Jackson et al. (1990). The results from these forms were used to detect any medical conditions or previous injuries that would cause serious risk to the participants during experimentation or compromise results. All participants had received a physical and completed regular fitness testing prior to the experiment as part of the requirements for being on active duty. All procedures were preapproved from the sponsoring institutional review board for the protection of human subjects.


Additionally, as Remsberg’s (2001) “crisis zone” only defined areas on the driver side of a vehicle, to define an MZ for the passenger side, pilot testing was done on multiple vehicles to determine the angle of the area deemed safest from threats presented by the driver. A 60° angle from the passenger side B-Pillar was determined to mitigate most threats; however, for research purposes, a more rigorous 45° angle was used in order to accommodate any prospective error associated with our video analysis (see Figure 1 for defined Mitigation Zones).


In order to investigate the influence of officer positioning on safety during a traffic stop, a number of positions that officers either take on initial approach or evolve into as the stop develops were established (see Figure 1 for designated officer positions). These positions were developed by senior author (WL), who has observed officers on traffic stops for over 40 years and instructed traffic stop conduct in an academy or clinical setting for over 25 years.



For each trial, participants began standing beside a police department cruiser. A confederate was seated in a 2004 Ford Taurus and both vehicles were aligned with the police cruiser off-center to simulate a roadside traffic stop (Figure 1) (Payton & Amaral, 1996; Perry, 1998). Before entering the warehouse, each officer was required to safety-check their firearm for an approved training gun with one round of Simunition, nonlethal training ammunition, and a magazine. They were also given a SOLO 915 Men’s wrist heart rate monitor, ear plugs, safety glasses, identification information, and an orange armband to indicate they had attended the safety-check portion of the study. The confederate driver was equipped with a handgun and Simunition ammunition.


Participants were video-recorded from an overhead position with aid of a scissor lift (Genie, Redmond, WA, USA). The third trial for each participant was video-recorded at 30 Hz and zoomed in sufficiently to prevent the need for panning (Flip Video Ultra HD, Flip Technology, Irvine, CA, USA). The area was marked off with one-meter strips to allow for calibrating screen pixels. All officers wore black shoes, and the warehouse floor was white tile, which aided our ability to detect foot positioning. Each video was digitized on a frame-by-frame basis using commercial software (Dartfish Prosuite 6.0, Dartfish, Alpharetta, GA, USA). XY coordinates for the front tip of the right and left shoes were determined, and the center of gravity (CG) was estimated as the equal distance between the right and left shoes. The video analysis software was also used to measure the designated MZ angles for both the passenger and driver side positions (Figure 1).


The primary purpose of this study was to examine the influence of officer position relative to the B-Pillar of a vehicle on tactical responses to a lethal threat in a traffic stop scenario. The secondary purpose of the study was to observe the responses, reactions, and