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The effects of conspicuous traffic enforcement on speeding behaviors: a study of speed reduction response.


In law enforcement, it is the purpose of speed enforcement, commonly referred to as "traffic radar enforcement," not only to detect motorists engaged in speeding and issue citations, or tickets, when appropriate, but to use this punitive method to alter the perceived risk associated with speeding behavior. Ideally, both enforcement and presence combine to increase the level of motorist obedience to speed limit laws. Traditionally, this is achieved by law enforcement professionals who use either a marked or unmarked law enforcement vehicle and employ a measuring device to record the speed of motorists passing through designated speed enforcement zones. Citations, or tickets, are then issued to motorists who jeopardize public safety by exceeding posted speed limits. One of the results of speed enforcement is the compliance of the motorist with posted speed limits as he/she passes through a speed enforcement zone and even after he/she does so.

This study seeks to determine the best method of using law enforcement presence to reduce or eliminate the speeding behavior of motorists. It is not designed to ascertain the best way to catch speeding motorists; rather, it seeks to learn the most effective method for positioning and displaying law enforcement vehicles to reduce future speeding infractions. In so doing, this study analyzes the speeding behavior of motorists when faced with the presence of either marked or unmarked law enforcement units, located at varying distances from the motorist, employing differing methods of concealment. Through an analysis of the motorists' speed adjustment when confronted with these various methods of speed enforcement, this study tries to identify the best method of using law enforcement vehicles in order to have the greatest impact on the 'Speed Reduction Response' behavior of motorists.


Speeding, quite clearly, is one of the major factors that contribute to traffic accidents and accident-related fatalities in the United States. According to the National Highway Traffic Safety Administration (NHTSA), the economic cost to U.S. citizens resulting from speeding-related crashes in 1999 was estimated at $28 billion. (1) That study also found that speeding accounted for approximately thirty percent of all fatal crashes in 2000, resulting in 12,628 deaths. (2) That trend has increased in recent years. In 2005, the United States Department of Transportation (USDOT) reported that speeding had become "a factor in nearly one-third of all fatal crashes." (3) The USDOT also estimated that speed-related car accidents cost U.S. citizens $44,193 per minute. (4)

The risk of injury and fatality to the motoring public increases as the speed limit increases. As the severity of a crash and its effect on the occupant(s) of a motor vehicle increase with speed, the effectiveness of occupant restraints and vehicle safety features decrease. Thus, the probability of death, disfigurement, or debilitating injury increases with higher rates of impact. Such consequences double for every ten miles per hour over fifty miles per hour that a vehicle travels. (5) An NHTSA report confirms this finding, stating that "more than half of fatal crashes occurred on roads with posted speed limits of 55 mph or more." (6) This is evident in North Carolina where, in 2005, "speeding was the leading violation in fatal crashes." (7) In fact, in North Carolina "one person is killed or injured in speed related crashes every 10.3 minutes," including the thirty-eight victims of fatal crashes in Buncombe County, the focus of this study? Given these statistics, it is easy to see that the ability for law enforcement to have a significant impact on the speeding behavior of motorists is of critical importance.


This study seeks to measure the 'Speed Reduction Response' (SRR) of motorists as they pass through a designated speed enforcement zone. Subject vehicles were paced as they passed through one of five such areas. During "pacing," a trained law enforcement officer matches the speed of a "target vehicle" and determines the speed of that vehicle by referring to his/her pre-calibrated and certified speedometer. In order to pace subject vehicles for this study, the authors used two unobtrusive, speedometer-calibrated vehicles: a 1998 white Ford XLT pickup and a 1994 silver, four-door Ford Taurus. Neither pace vehicle had any markings or other indicators that would cause it to be noticed by motorists. Pacing was conducted at a discrete distance, and both pace vehicles were operated by the authors who were then instructors at the North Carolina Justice Academy and sworn law enforcement officers. The pace drivers had extensive traffic law enforcement-related experience, and the lead pace car driver was a certified radar and time-distance instructor for the state. A speed enforcement unit, or stimulus, was positioned and maintained by a third law enforcement professional who possessed extensive, specialized experience and training in traffic enforcement. The marked vehicle was a 2000 white, four-door Ford Crown Victoria, equipped with a standard forward and rear radar antenna and overhead strobe lights, with the Sheriff's Department's logo and other law enforcement graphic identifiers appearing in blue and silver relief. The unmarked unit used in this study, a 2002 graphite, four-door Chevy Impala with a concealed light package and no visible radar antennas, was driven by the same operator.

The location for this study was chosen because it represented typical highway conditions and an environment wherein traffic enforcement occurs. As either state or local law enforcement officers or agents who were trained, experienced, and sworn within the jurisdiction where this study was conducted, the authors had the authority to operate law enforcement-related equipment and to directly observe the behavior of motorists in a manner that would not otherwise be possible. The study was conducted over a two-day period during morning hours. Traffic congestion was moderate during this non-rush hour time frame. Speed readings were recorded on Interstate 26 near Asheville, North Carolina, where the posted speed limit is sixty-five miles per hour. The two pace car drivers documented 300 speed readings as their subject vehicles passed through each of the five speed enforcement zones. Subject vehicles were selected at random, with no consideration given to original traveling speed, make, model, operator, or type of vehicle.

For the purpose of this study, both commercial and non-commercial vehicles were paced. The law enforcement vehicle, or stimulus, was positioned according to the level of presence and surprise desired within a particular scenario. The weather on the first day of the study was clear with temperatures in the low seventies. A slight haze appeared on the second day, but it did not obscure motorist vision and cleared up by late morning. Temperatures were again in the low seventies. Both the type of vehicle used, marked or unmarked, and the ability of the law enforcement professional to select the location for the vehicle were, by state law and departmental policy, left to the discretion of the agency and/ or the operator. The authors recognize that in some jurisdictions options related to the type of law enforcement vehicle used and the positioning of that vehicle may be restricted by state law or organizational policy. For the purpose of this study, and in the interest of universalizing the results, elements related to law enforcement vehicle type (marked and unmarked) and position (clearly visible and concealed) were explored.


The three independent variables in this study are: (1) the zone through which the motorist passed; (2) the presence or lack of a surprise stimulus; and, (3) the level of law enforcement presence encountered by the motorist. The dependent variable is the speed of the motorist measured in statute miles per hour.


For the purpose of this study, speed enforcement zones were measured and clearly marked to enable the drivers of the pace cars to correctly document speeds within those particular zones. The zone areas were designated as follows:

Zone 1: In this zone, the pace car originally made contact and began pacing the target vehicle. This area was situated one statute mile away from the point of contact zone where the stimulus of the law enforcement vehicle was present. Speeds recorded in this zone represent the original traveling speed of the motorist.

Zone 2: This zone was the point of contact where the law enforcement vehicle had been placed, and where it was visible to the motorist. Speeds measured in this zone represent the speed after the driver had a chance to respond to the presence of the law enforcement vehicle.

Zone 3: This zone was exactly one-quarter statute mile past the point where the motorist made contact with the stimulus of the law enforcement vehicle.

Zone 4: This zone was exactly one-half statute mile beyond the location where the motorist made contact with the stimulus of the law enforcement vehicle.

Zone 5: This zone was exactly one statute mile past the point where the motorist made contact with the stimulus of the law enforcement vehicle. Speeds recorded in this zone represent the final traveling speed of the motorist.

Surprise/Non-Surprise Element

The surprise element was simply a measure of the reaction time a motorist would have to respond to the presence of the law enforcement officer engaged in speed enforcement. To create the element of surprise, both the marked and unmarked patrol vehicles were hidden from the motorist's view, allowing them to be seen only when the driver was parallel with the officer's vehicle. The non-surprise variable was one where the officer and the patrol vehicle could be seen at least one-half mile prior to the point of contact. This would give the motorist sufficient time to process what he/she observed and to respond accordingly. A representation of each position and how the element of surprise was employed in this study is shown in Figures 1-4.

Levels of Presence

As indicated in Figures 1-4, there were six levels of presence. Each was designated to simulate how a typical traffic enforcement officer would position his/her vehicle while engaged in speed enforcement.

Levels of Presence Involving Surprise

When the "surprise" variable was involved, the first level of presence was a "Marked and Unmarked Car Concealed in Median." This involved a patrol vehicle being parked behind a bridge abutment and concealed by foliage (Figure 1). The patrol vehicle became highly visible as the motorist passed a location parallel with that vehicle. It was parked with its back facing traffic, and the officer's intent of running radar was clearly indicated.


In the "Unmarked Car On Side of Road" position, the patrol vehicle was moved closer to the road in an area that made the intent of the officer somewhat ambiguous (Figure 2). It was visible on the side of the road as if the law enforcement officer had just pulled over to write a ticket or to assist a stranded motorist. The surprise element was in effect, but it was not as pronounced, since the position of the patrol vehicle was closer to the road and positioned away from concealment.


Levels of Presence Involving Non-Surprise As mentioned earlier, "non-surprise" describes the scenario in which a law enforcement officer's vehicle was visible from the distance of one-half statute mile. This area can be found in the "Marked and Unmarked Car in Median" title. This involved a patrol vehicle parked in the median facing traffic, with both the car and tires angled to allow for a rapid entry into traffic, a commonly encountered traffic enforcement position (Figure 3).


KEVIN W. DOWLING, a former Master Police Officer in Wilmington, North Carolina, as well as a former instructor/coordinator at the North Carolina Justice Academy, is currently a Senior Protection Analyst for the Board of Governors of the Federal Reserve Bank. ERIC HOLLOMAN, a former member of the Charlotte-Mecklenberg Police Department in North Carolina and a former instructor/coordinator at the North Carolina Justice Academy, is Chair of Criminal Justice Technology, Cyber Crime Technology and Basic Law Enforcement Training at Guilford Technical Community College in Jamestown, North Carolina.

The second variable under non-surprise involved a marked car on the right side of the road. Here, the patrol vehicle was parked facing away from traffic to the right-hand side of the road. This is the classic "ticket writing" position. The patrol vehicle was not running any of its emergency equipment (Figure 4).



The first analysis of the data involved the SRR of motorists. The SRR was calculated by subtracting the original speed of the motorist documented in Zone 1 from the final recorded speed of that vehicle as it passed through Zone 5. This permitted a measurement index that was not impacted by the speed with which the motorist was originally operating his/her vehicle. The SRR measures the overall effect that a particular type of speed enforcement presence has on speeding behaviors one statute mile after the stimulus is encountered. This controls more closely for the fact that motorists traveling at a greater speed usually slow down at a significantly higher rate than those who are driving closer to the posted speed limit. If not accounted for, this tends to skew the speed reduction data in the research. Since the purpose of this study is to measure the reduction of speed of all motorists, not simply high-rate speeders, the SRR is a more appropriate method to measure change in driving behavior over a greater distance.

The overall greatest amount of speed reduction is found in cases where the variable of surprise was present. The highest-rated category for speed reduction is evident in the "Surprise, Marked Car Concealed in Median" category (SRR= 6.1), followed by the "Surprise, Unmarked Car Concealed in Median" category (SRR=5). These were followed by the two highest "Non-Surprise" categories, "Non-Surprise, Marked Car in Median" (SRR=3.4), and "Non-Surprise, Unmarked Car in Median" (SRR=2.5). The two lowest SRR ratings were found in the "Surprise, Unmarked Car on Side of Road" category (SRR=I.5), and "Non-Surprise, Marked Car on Side of Road" category (SRR =.7).

A series of 2 (Surprise, Non-Surprise) X 3 (Levels of Presence 1, 2, and 3) analysis of variances (ANOVAs) were conducted to determine the impact of both the element of surprise and levels of presence on the SRR of motorists. The main effects of surprise were significant in all zones when the speed of motorists within those zones was subtracted from the original speed recorded in Zone 1. This included Zone 3, F (1,58) = 7.79, p < .01; Zone 4, F (1,58) = 9.98, p < .01; and, Zone 5, F (1,58) = 17.70, p < .01. The results also revealed that the significance of the f-ratio under the variable of surprise increased as motorists passed through subsequent speed enforcement zones after encountering the stimulus. Since the f-ratio represents a measure of the variance between two independent samples, this increase demonstrates the ability of the stimuli to impact the SRR of motorists across subsequent speed enforcement zones, not just within the zone in which the stimulus was encountered. This is shown in the following results: Zone 3 (p = .007), Zone 4 (p = .003), and Zone 5 (p = .000). However, there was no significant effect noted concerning levels of presence within any of the zones: Zone 3, F (1,58) = 1.34, p < .01; Zone 4, F (1,58) = 2.30, p < .01; and, Zone 5, F (1,58) = 2.20, p < .01. In addition, there is no evidence of any significant interaction effects between the two independent variables.


This study shows that the efforts of law enforcement professionals to change the future speeding behaviors of motorists have a strong ally in the element of surprise. The results indicate a significant increase in SRR when surprise is employed to achieve that goal. This is true even if an unmarked unit is present in the speed enforcement zone. The implication of this finding is clear. When a speed enforcement unit surprises motorists, they tend to respond by reducing their speed at a higher level over a greater period of time. This is true even when the motorist is not speeding. As the finding of this study indicates, law enforcement officers can increase their effectiveness in reducing the future speed of motorists by more than 400 percent if they are positioned where the motorist is surprised by their presence. Whether this is due to a sudden adrenaline rush, a feeling of guilt, or some other factor cannot be determined. It should also be noted that the speed of motorists when they are surprised continues to decrease as they travel farther away from the location of the law enforcement unit. This implies that when a speed enforcement unit is suddenly encountered, it takes a motorist time to process what he/she observed. The SRR is a seemingly natural reaction, one that causes motorists to continue to slow down even after they have passed a law enforcement unit.

While the data analyzed here has yet to be the subject of additional research, it is recommended that law enforcement agencies carefully consider the potential impact of non-conspicuous traffic enforcement on future speeding behaviors of motorists. The intentional positioning of law enforcement vehicles where they can have the greatest impact on public perception and motorist behavior could increase the benefits realized from the practice of speed enforcement by reducing speed-related tragedies.


(1) National Highway Traffic Safety Administration, "Traffic Safety Facts, 1999: A Compilation of Motor Vehicle Crash Data from the Fatality Analysis Reporting System and the General Estimates," in National Highway Traffic Safety Administration Report (December 2000), (accessed January 7, 2007), 169.

(2) Ibid.

(3) United States Department of Transportation, "Think Fast," in National Highway Traffic Administration Report (August 2005), NHTSA/Traffic%20Injury%20Control/Articles/Associated%20Files/think/pdf (accessed March 3, 2008), 1.

(4) Ibid.

(5) Ibid.

(6) National Highway Traffic Safety Administration, "Traffic Safety Facts, 1999: A Compilation of Motor Vehicle Crash Data from the Fatality Analysis Reporting System and the General Estimates," in National Highway Traffic Safety Administration Report (December 2000), http://www.nrd.nhtsa.dotgov/pdf/nrd-30/NCSA/TSFAnn/TSF1999.pdf (accessed January 7, 2007), 43.

(7) North Carolina Division of Motor Vehicles, "North Carolina 2005 Traffic Crash Records," Traffic Branch Records, North Carolina Department of Transportation, Raleigh, North Carolina (2005), 3.

(8) Ibid., 7, 96.

J.B. WATSON, JR., is an Associate Professor of Sociology at Stephen E Austin University in Nacogdoches, Texas. WALTER H. SCALEN, JR., is an Assistant Professor of Criminal Justice at Stephen E Austin University in Nacogdoches, Texas.
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Author:Dowling, Kevin W.; Holloman, Eric
Publication:International Social Science Review
Geographic Code:1USA
Date:Sep 22, 2008
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