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ois
Law
Enfo
rcement Training and StandardsB
oard
Executive Institute
Law Enforcement Executive
Critical Issues in Police Discipline
Vol. 13, No. 1 • March 2013
98 Law Enforcement Executive Forum • 2013 • 13(1)
The Influence of Officer Positioning on Movement During a Threatening Traffic Stop ScenarioWilliam J. Lewinski, PhD, Force Science® InstituteJennifer L. Dysterheft, Graduate Student, Minnesota State University, MankatoDawn A. Seefeldt, MA, Force Science® InstituteRobert W. Pettitt, PhD, Minnesota State University, Mankato
IntroductionConducting 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 offi-cers in the United States, were not developed from scientific research. As noted by Justice Scalia, there is a paucity of research on offi-cer 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 passen-ger 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 vehi-cles 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
Law Enforcement Executive Forum • 2013 • 13(1) 99
zone” or MZ is an area where the officer is at a position of reduced risk because the configu-ration of the vehicle being stopped impairs or restricts the driver’s visual access or weapon alignment on the officer. The MZ on the driv-er’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 clench-ing 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, accord-ing 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 indi-viduals (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, star-tle 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 posi-tions 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 reac-tions, tactical responses, and movements made by the officers. In particular, reaction and movement times were measured in rela-tion 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 reac-tions and movement speed. Prior to this study, there had been no formal assessment of officer reactions in a threatening traffic stop scenario.
Methods
Participants
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 enforce-ment 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
100 Law Enforcement Executive Forum • 2013 • 13(1)
an investigator in the warehouse. All partici-pants completed informed consent waivers before entering the warehouse.
Participants also completed a health screen-ing and fitness level questionnaire (range 0 to 10) (George, Stone, & Burkett, 1997). The par-ticipants’ 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 con-ditions or previous injuries that would cause serious risk to the participants during experi-mentation or compromise results. All partici-pants 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 pre-approved 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 vehi-cles 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.
Equipment
For each trial, participants began standing beside a police department cruiser. A confed-erate was seated in a 2004 Ford Taurus and both vehicles were aligned with the police cruiser off-center to simulate a roadside traf-fic 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 train-ing ammunition, and a magazine. They were also given a SOLO 915 Men’s wrist heart rate monitor, ear plugs, safety glasses, identifica-tion 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 Simuni-tion 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 commer-cial software (Dartfish Prosuite 6.0, Dartfish, Alpharetta, GA, USA). XY coordinates for the front tip of the right and left shoes were deter-mined, and the center of gravity (CG) was estimated as the equal distance between the right and left shoes. The video analysis soft-ware 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 rel-ative 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
Law Enforcement Executive Forum • 2013 • 13(1) 101
movements made by the officers. These times were used to observe whether or not one posi-tion might be deemed safer than others. Using the digital video analysis, we determined times for the following events: Driver Move-ment Initiation, Driver Weapon Presentation, Officer Reaction Initiation, Mitigation Zone Reached, Officer Weapon Presentation, Driver Weapon Discharge, Officer Weapon Dis-charge, and, if applicable, Officer Neutraliza-tion Attempt (see Table 1 for event definitions for data analysis and Figure 1 for Mitigation Zone).
Procedures
Prior to beginning the experimental phase, participants were informed that they would be completing a number of trials of a traffic stop scenario that may or may not escalate. Participants were neither informed of the exact number of trials nor when nor how the traffic stop would escalate in order to ensure that his or her reactions were as close to natu-ral as possible. Using a predetermined script, the same instructor directed all participants,
one at a time, that the scenario was a roadside traffic stop occurring because the driver exceeded the posted speed limit by 10 mph. Participants were instructed that once they approached the driver’s vehicle, they must stand with the toes of at least one foot on a line at a predetermined angle, taped on the ground, and were not to move from that align-ment unless necessary. Participants were also directed to keep their hips and torso aligned with the tape on the floor relative to the vehi-cle. These angles consisted of 45°, 90°, 180° in Front of the B-Pillar on the driver’s side, and 180° Behind the B-Pillar on the driver’s side, in addition to 45° in Front of the B-Pillar on the passenger’s side or a self-selected posi-tion on the driver’s side (Figure 1). The use of predetermined positions was to preserve internal validity, whereas the addition of the self-selected position was to preserve external validity. Heart rate measures were taken upon officers’ arrival (for baseline), after entering the warehouse and receiving instructions for the scenario procedures, and immediately following each of the traffic stop trials. Heart rates are expressed relative to the officer’s
Figure 1. Traffic Stop Simulation and Positioning
Participant positioning: a. 90˚, b. 45˚, c. 180˚ Behind the B-Pillar, and d. 180˚ in Front of the B-Pillar on the driver’s side, as well as e. 45˚ on the passenger’s side. Self-Selected Stance not displayed due to participant variability.n = sample size (percentage of overall sample)
102 Law Enforcement Executive Forum • 2013 • 13(1)
Tab
le 1
. Eve
nt
Def
init
ion
s fo
r D
ata
An
alys
is w
ith
Po
siti
on
Mea
n a
nd
Sta
nd
ard
Dev
iati
on
Eve
nt T
ime
(s) M
(SD
) by
Posi
tion
Eve
nt T
itle
Cod
ing
Def
init
ion
90°
(D
rive
r’s
Si
de)
45°
(D
rive
r’s
Sid
e)
18
0°
(Dri
ver’
s
Sid
e)
180°
B
ehin
d
B-P
illar
(D
rive
r’s
Sid
e)
45°
(Pas
seng
er’s
Si
de)
Se
lf-
Sele
cted
(D
rive
r’s
Sid
e)
O
vera
ll
Dri
ver
Mov
emen
t In
itia
tion
Any
mov
emen
t or
shif
t in
the
dri
ver’
s bo
dy
that
in
dic
ates
the
dri
ver
is p
rese
ntin
g th
eir
wea
pon.
Thi
s ev
ent r
epre
sent
s th
e ze
ro ti
me
poin
t to
the
even
ts
belo
w.
NA
NA
NA
NA
NA
NA
N
A
Dri
ver
Wea
pon
Pres
enta
tion
The
poi
nt in
tim
e w
hich
the
dri
ver’
s gu
n is
fully
pr
esen
ted
in o
pen
view
of t
he o
ffic
er a
nd n
o lo
nger
in
mot
ion
upw
ard
s.
0.38
(0
.12)
0.33
(0
.1)
0.32
(0
.06)
0.34
(0
.09)
0.34
(0
.06)
0.36
(0
.08)
0.34
(0
.09)
Off
icer
Rea
ctio
n In
itia
ted
A
ny m
ovem
ent o
r sh
ift i
n th
e of
fice
r’s
bod
y th
at
ind
icat
es th
eir
reac
tion
(to
the
dri
ver’
s w
eapo
n pr
esen
tati
on) w
as b
egin
ning
.
0.37
(0
.13)
0.37
(0
.17)
0.36
(0
.10)
0.35
(0
.10)
0.37
(0
.13)
0.36
(0
.13)
0.37
(0
.13)
Mit
igat
ion
Zon
e R
each
ed
The
pre
cise
fram
e/po
int i
n ti
me
in w
hich
the
offi
cer’
s en
tire
bod
y w
as w
ithi
n th
e d
esig
nate
d M
itig
atio
n Z
one.
2.27
(0
.25)
2.46
(0
.65)
2.
43
(0.7
5)2.
04
(0.3
9)1.
5
(0.5
2)b
2.21
(0
.68)
2.12
(0
.67)
Off
icer
Wea
pon
Pres
enta
tion
T
he p
oint
that
the
offi
cer
had
fully
dra
wn
thei
r w
eapo
n an
d h
ad th
eir
wea
pon
paus
ed a
nd a
ligne
d o
n ta
rget
.
1.96
(0
.47)
1.93
(0
.71)
2.01
(0
.45)
1.87
(0
.56)
1.95
(0
.81)
1.93
(0
.49)
1.95
(0
.60)
Off
icer
Neu
tral
izat
ion
Att
empt
If
the
offi
cer
atte
mpt
ed to
neu
tral
ize
the
wea
pon,
the
tim
e th
e of
fice
r’s
hand
mad
e co
ntac
t wit
h th
e d
rive
r’s
gun.
0.53
0.59
(0
.13)
0.46
(0
.10)
NA
aN
Aa
0.47
0.53
(0
.16)
Wea
pon
Dis
char
ge
(Off
icer
) T
he p
oint
in ti
me
the
offi
cer’
s gu
n w
as fi
rst f
ired
. 2.
20
(0.0
5)1.
99
(0.5
9)2.
07
(0.4
7)2.
44
(1.4
7)2.
15
(0.9
2)2.
11
(0.5
2)2.
17
(0.8
6)
Wea
pon
Dis
char
ge
(Dri
ver)
T
he p
oint
in ti
me
the
dri
ver’
s gu
n w
as fi
rst f
ired
. 0.
57
(0.1
4)0.
50
(0.1
7)
0.55
(0
.20)
0.53
(0
.16)
0.52
(0
.14)
0.53
(0
.25)
0.53
(0
.18)
Not
e: M
= a
vera
ge; S
D =
sta
ndar
d d
evia
tion
a Not
all
part
icip
ants
in th
is p
osit
ioni
ng a
ttem
pted
to n
eutr
aliz
e th
e d
rive
r.b T
his
tim
e w
as s
igni
fica
ntly
fast
er in
com
pari
son
to a
ll of
the
othe
r po
siti
ons,
exc
ept 1
80°
Beh
ind
the
B-P
illar
Law Enforcement Executive Forum • 2013 • 13(1) 103
age-predicted maximal heart rate using the following equation (Tanaka, Monahan, & Seals, 2001):
Age Predicted Heart Rate Maximum = 208 - (Age * 0.7).
Participants were instructed that they could begin the trials when the researcher told them to begin, and the trials would end when the researcher blew the whistle. All trials began at the driver’s side door of the police vehi-cle. Officers then walked to either a prede-termined position or a self-selected position relative to the confederate’s vehicle. The first two trials consisted only of a verbal confron-tation lasting 45 seconds. The confederate driver’s script included his proclamation that he was a sovereign nation, no longer a part of the United States, and therefore was not required to follow U.S. laws. The confederate used a given script consisting of argumenta-tive phrases such as “Do you even know what you’re doing?,” “I am in my own nation,” and “I don’t think you understand—I need to leave.” He was also supplied with two pieces of documentation: (1) a homemade “convey-ance pass” and (2) declaration of his sover-eign nation status; however, he did not have any state-issued identification, registration, proof of insurance, or a driver’s license. The first two trials were intended to distract the participants from the true intent of the study: to evaluate their response to a lethal threat during a traffic stop.
The third trial began with a verbal exchange, similar to the first two trials. The trial esca-lated when the confederate pulled and fired a weapon multiple times at the participant. This trial was video-recorded and used for move-ment analysis of the participant’s response to the deadly threat. Following each partici-pant, the warehouse was ventilated between trials to remove the excess smoke created by the firearms and to prevent participants from detecting that there would be gunfire during the experiment. The participants also were debriefed as to the true intent of the study by a retired police psychologist and were given
the opportunity to review footage of the third trial.
Data Analysis
The last seven events in Table 1 represent the dependent variables. The times for each of the seven variables were found by subtracting the time at which the event took place in each video from the time in the video for Driver Movement Initiation. A second investigator evaluated a total of 22 participants (~25% of the sample) for the purpose of establishing inter-rater reliability. These data were evalu-ated using intraclass correlation coefficient (ICC) and coefficient of variation (Hopkins, 2000). Each dependent variable was exam-ined using a one-way ANOVA with repeated measures and Bonferroni-adjusted post-hoc testing. The criterion used to reject the null hypothesis was p < 0.05. All descriptive statis-tics are reported as mean ± SD.
ResultsEach traffic stop trial evoked higher heart rate responses in comparison to pre-trial measures (Figure 2) (F = 163, p < 0.01). The third trial evoked the highest heart rate responses in comparison to the other trials, which would indicate the third trial evoked a genuine startle response. Inter-rater reliability for the digital analysis of time for each event (Table 1) was extremely high (ICC = 0.99 and coefficient of variation = 2.85%). No time differences between positions were observed for Driver Weapon Presentation (F = 0.75, p = 0.43), Driver Weapon Discharge (F = 0.31, p = 0.90), or Offi-cer Reaction Initiated (F = 0.38, p = 0.99). Like-wise, no time differences were found between positions for Officer Weapon Presentation (F = 0.05, p = 0.99), Officer Neutralization Attempt (F = 0.54, p = 0.67), or Officer Weapon Dis-charge (F = 0.59, p = 0.71) (Figure 3).
In each of the trials, all officers approached the confederate’s vehicle with their weapons holstered. For all of the experimental trials, the confederate was able to draw and aim his gun at the officers; however, 12 officers made
104 Law Enforcement Executive Forum • 2013 • 13(1)
an attempt to neutralize the confederate’s weapon, and three were successful. One offi-cer deflected the confederate’s weapon while drawing and discharging their own weapon, whereas another officer applied a defensive choking maneuver. Both officers prevented the driver from firing his weapon (NB, the researcher with the whistle, ended the trials to avoid injuries to the confederate and offi-cers). A third officer was able to sweep aside the confederate driver’s gun at the time of discharge while firing their own. A total of 81 of 93 (87%) officers engaged the confeder-ate driver by attempting to neutralize and/or by drawing their weapon and returning fire. A total of nine of 93 (10%) officers neither attempted to neutralize nor engage the driver and simply retreated from the threat. Of the officers self-selecting their approach (n = 13), five chose the 180° Behind the B-Pillar (posi-tion c, Figure 1), three stood in the 45° Driv-er’s Side (position b, Figure 1), four selected a
45° Behind the B-Pillar, and one chose the 180° in Front of the B-Pillar (position d, Figure 1).
Analysis of the videos revealed two primary startle responses regardless of positioning to the confederate vehicle: (1) a response of the non-weapon hand “guarding” the face and back pedaling while drawing their weapon and returning fire (n = 53), and (2) a reaction of side-stepping or carioca stepping to retreat, followed by drawing their weapon and returning fire (n = 19). Mean times to reach the MZ for the startle responses were very simi-lar (backpedaling: 2.10 ± 0.73 s; side-stepping: 2.16 ± 0.52 s). A total of 17 of the 93 officers did not reach the MZ as defined in Figure 1. In analyzing the two primary startle responses, nine (17%) of the participants who backped-aled and two (11%) of those who side-stepped did not reach the MZ.
Figure 2. Heart Rate Responses (M ± SD) Across Time
Figure 2. Heart rate responses (M ± SD) across time. Raised letters denote significant differences (P < 0.05), where a is significant from initial and pre-trials and b is significant from all other trials.
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Initial Post Instruction/ Pre-Trials
Post Trial 1 Post Trial 2 Post Trial 3
Perc
enta
ge H
Rm
ax
Changes in Officer Percentage HRmax During Trials
Average
Maximum
Minimum
a a a, b
Note: Raised letters denote significant differences (p < 0.05), where a is significant from initial and pre-trials and b is significant from all other trials.
Law Enforcement Executive Forum • 2013 • 13(1) 105
Video analysis also revealed that when partici-pants drew their weapon, either before (n = 39) or after (n = 20) reaching the MZ, influenced the amount of time it took to reach the MZ. The participants who began drawing their weapon after they had already reached the MZ (2.04 ± 0.41 s) were faster at reaching the MZ (F = 5.99, p = 0.02) in comparison to offi-cers who began drawing their weapon early in their retreat (2.43 ± 0.64 s). Participants who did not make it to the MZ were not included in data comparison due to failure to qualify for criterion. Additionally, participants who were positioned on the 45° Passenger Side were not included in the data comparison because there was a lack of distinguishable difference in the two variables being compared as a result of the close proximity of the passenger side MZ.
Positioning (Figure 1) effected the time to reach the MZ (F = 5.82, p < 0.01). The MZ
was reached significantly faster (M = 0.56 s) when beginning in the 45° Passenger Side position in comparison to all other positions, with the exception of 180° Behind the B-Pillar (Figure 1). The 180° Behind the B-Pillar posi-tion was the fastest of the positions beginning on the driver’s side; however, the difference was not statistically significant (Table 1). For all of the officers, the dependent variables noted in Table 1 were evaluated.
DiscussionThe primary purpose of this study was to examine the influence of officer position rela-tive to the B-Pillar of a vehicle on any adher-ent safety elements of the officer’s tactical responses to a lethal threat in a traffic stop scenario. A secondary purpose of the study was to observe the responses, reactions, and
Figure 3. Position and Event Time (s) Comparisons (M ± SD)
Figure 3. Position and event time (s) comparisons (M ± SD)
*denotes significant value
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Mitigation Zone Reached
Weapon Discharge (Officer)
Officer Weapon Presentation
Weapon Discharge (Driver)
Officer Reaction Initiated
Driver Weapon Presentation
Time (s) from Driver Movement Initiation
Position Timeline Comparison
Passenger Self-Selected
Driver 180° Behind B-Pillar Driver 180° in Front of B-Pillar
Driver 90° Driver 45°
(n = 17)
(n = 16)
(n = 15)
(n = 13)
(n = 15)
(n = 18)
*
*Denotes significant value
106 Law Enforcement Executive Forum • 2013 • 13(1)
movements made by the officers during a threatening traffic stop scenario.
For each participant, our confederate was able to aim and, in most cases (90 of 93), dis-charge his pistol at the officer. The heart rate data indicates that a genuine startle response was evoked in the third trial, reaching an average of 70% age-predicted heart rate maxi-mum (Figure 2) for which a 70% maximum is regarded as a high level of aerobic exercise (Sime, 1985). As such, the preceding two trials effectively distracted the officers from our true purpose of the study: to evaluate their realis-tic response to the threat of lethal force during a traffic stop scenario. No differences between positions were observed for the time it took the confederate to present and discharge his pistol. Thus, we are confident our comparison of response times from the various positions relate to the mechanics of the positions rela-tive to the vehicle and is not due to the timing differences of our confederate’s actions. More-over, we observed high intra-rater reliability of our timing method, reducing measurement error as a likely cause for unrealistic findings. All self-selected trials were completed on the driver’s side with a majority of officers stand-ing in one of the preselected experimental positions, with 180° Behind the B-Pillar posi-tion being the most commonly selected. As such, we are confident the results of this study reflect how police officers would realistically position themselves at an apprehended vehi-cle and respond to an actual lethal threat.
One of the primary observations made during our study were the participants’ startle responses upon threat presentation. Although it was observed that officers who backped-aled and side-stepped had very similar times in reaching the MZ, a considerably higher percentage of those who backpedaled were unsuccessful in reaching the MZ. We also noted that officers who backpedaled exposed their center of mass and head to the driver for a greater amount of time. These reactions seem to have little to do with previous train-ing and are more heavily based on human instincts. One of the most common gestures
made during officers’ startle responses was the “blocking” movement in which they raised their hands or arms to shield themselves from the gun and then began to backpedal while drawing their weapon.
Officers are trained to neutralize a suspect’s weapon in very close proximities rather than retreat and try to draw their own because drawing their own simply takes too much time (Adams et al., 2009; Davis, 2006). How-ever, this neutralization was only seen in three of 93 participants, while the remaining 90 participants were often shot multiple times. Although nine officers made an attempt to neutralize the driver’s weapon, none fol-lowed through with or finished the attempt, resulting in the need for retreat and further exposure to the driver’s gunfire. Such an observation reaffirms the necessity for officers to engage regularly in tactical training along with visualization strategies toward neutral-izing a weapon in close proximity with this type of assault during a routine traffic stop.
The other notable observation made on officer retreat times was the significant difference in the amount of time it took officers to reach the MZ. Officers who waited until after they had already reached the MZ to draw their weap-ons were able to retreat 0.39 s faster than if they were to simultaneously draw and retreat. This difference can be attributed to the more com-plex motor movement and attention resources needed to draw and retreat as opposed to simply retreating and then engaging.
When examining the influence of position on officers’ response times to a threat during a traffic stop, we observed that officers who approached the vehicle on the passenger side were able to reach the MZ by an average of 0.56 s faster than if they were to approach on the driv-er’s side, with the exception of officers starting at a 180° angle behind the vehicle’s B-Pillar on the driver’s side. Therefore, approaching the passenger side of a vehicle during a routine traffic stop allows officers to reach a zone—con-sidered to mitigate potential threats presented by the driver—much more quickly.
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According to previous research (Lewinski, 2000), the time it takes a suspect in the driv-er’s seat to pull a concealed weapon and fire at their target is 0.25 s on average, with the fastest recorded time being 0.15 s. The results of this study demonstrate slightly longer shooting times as the driver took time to align his weapon to the moving center mass of the participant, resulting in a mean Weapon Dis-charge (Driver) time of 0.53 ± 0.18 s (Table 1). Factoring in the average time it took offi-cers to react to the driver’s movement (M = 0.37 ± 0.09 s) shows officers are left with less than 0.20 s to either present and discharge their weapon or reach the MZ. As previously noted, it was demonstrated that officers who pulled their weapon after they were already in the MZ were able to get there 0.39 s faster than officers who pulled their weapon during retreat from the driver’s side window. Addi-tionally, officers positioned on the driver’s side of the vehicle took an average of 2.29 ± 0.60 s to reach the MZ, while officers who approached on the passenger side were able to reach the MZ in an average of 1.50 ± 0.52 s, thus possibly giving the officers an additional 0.50 s to reach safety. Such a small window of time could mean the difference between life and death in the field. Prior research indicates that once a target is acquired, it takes 0.25 to 0.36 s, dependent upon the type of weapon and speed of trigger stroke, to fire off just one additional round (Lewinski, 2002). Given the current findings of the study, a suspect could fire two to three shots at a retreating officer before the officer is able to get to safety, empha-sizing the importance of officer responses to the presentation of a deadly threat.
ConclusionThis is the first study to systematically eval-uate police officer responses to the threat of lethal force during a routine traffic stop. Our findings indicate that the positions most com-monly used during driver’s side traffic stop procedures fail to adequately protect offi-cers against the threat of lethal force. Con-versely, a robust finding of the study was that approaching a vehicle on the passenger side
during a traffic stop is the safest option for officers because they can reach the Mitigation Zone faster and spend less time in the line of fire. We also observed officers who waited until reaching the MZ to draw their weapon retreated more rapidly than those who drew their weapon simultaneously to retreat. These two findings show the only two significantly influential approaches officers can use to max-imize their safety when conducting a routine traffic stop. If officers, regardless of the cur-rent findings, still choose to approach vehi-cles on the driver’s side during a traffic stop, the development of skills in close proximity neutralization and visualization strategies to increase officers’ chances of survival in a threatening situation is highly recommended.
AcknowledgmentsWe are indebted to Scott Buhrmaster, who served as the confederate for this study, to Patricia Thiem for coordinating the partici-pants through the trials, and to Dr. Jeff Martin for his assistance in the collection of sup-portive research. We also would like to thank Sergeant Craig Allen, the Hillsboro Police Department Force Tactics Team, and the Hillsboro Police Department for their efforts in coordinating the logistics of the study and recruiting officers to serve as participants.
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Dr. William J. Lewinski ([email protected]) is a behavioral scientist specializ-ing in law enforcement-related issues. He has a PhD in Psychology with a con-centration in Police Psychology and is a Professor Emeritus at Minnesota State University, Mankato, where he taught for nearly three decades. He is the founder and director of the Force Science Institute, Ltd. Dr. Lewinski’s research interests are in human behavior in force encounters, focusing on attention/reaction, percep-tion, attention/memory, and judgment. His research and expertise have been pub-lished in peer-reviewed journals, national law enforcement publications, websites, and e-newslines, and have also been high-lighted on 48 Hours Investigates, BBC’s Panorama, Discovery Channel Canada, and CNN News.
Jennifer L. Dysterheft (jennifer.dysterheft@ mnsu.edu) is a graduate student in the Department of Human Performance: Exer-cise Physiology at Minnesota State Uni-versity, Mankato, and a graduate research assistant at the Force Science Institute. She received her baccalaureate degree in Exer-cise Science from Minnesota State Uni-versity, Mankato. Her primary research interests are biomechanics and kinesiology, human movement and performance, and movement analysis.
Dawn A. Seefeldt ([email protected]) has a Master of Arts in Clinical Psychology from Minnesota State University, Mankato, and is cur-rently a research assistant at the Force Science Institute. Dawn received two baccalaureate degrees in Psychology and Criminal Justice from the University of South Dakota. Her research interests are use-of-force dynamics, human per-formance, and behavioral interventions.
Dr. Robert W. Pettitt ([email protected]) is an exercise scientist at Minnesota State University, Mankato, who has worked in various capacities of sports performance and strength and conditioning across the U.S. He has a PhD in Exercise Science with an emphasis in Exercise Physiology from the University of Utah. Bob is a certified strength and conditioning specialist with the National Strength and Condition-ing Association (NSCA) and a certified athletic trainer with the National Ath-letic Trainers’ Association (NATA). He is an expert in the assessment of endur-ance athletes and has published over 50 research articles/abstracts on the valid-ity of endurance exercise measurements, along with the prevention and treatment of musculoskeletal injuries associated with distance running. His textbook, Exercise Physiology Laboratories (2009), is available through Kendall-Hunt Pu.
Contact Information William Lewinski Force Science Institute 124 E. Walnut Street, Suite 120 Mankato, MN 56001 [email protected] (507) 387-1290 Fax: (507) 387-1291
Research AffiliationsForce Science® Institute 124 E. Walnut Street, Suite 120 Mankato, MN 56001
Minnesota State University Human Performance Lab 1400 Highland Center Mankato, MN 56001
