Most people can recall reading or hearing of examples of routine traffic enforcement stops that resulted in the dramatic apprehension of wanted criminals, or the accidental discovery of criminal activity. Most notable of the examples is the Oklahoma Highway Patrol’s apprehension of Timothy McVeigh, who was stopped for speeding and no license plate following the bombing of the Federal building in Oklahoma City. Despite the many anecdotal accounts and dramatic examples, little effort has been devoted to quantifying the contributions of traffic officers to the general mission of law enforcement.

BACKGROUND
The Grand Prairie, Texas, Police Department has a record-keeping system that can measure the effects of traffic enforcement on criminal activity as well as on traffic safety. That feature permits the attribution of arrests to the initiating officer activity (e.g., traffic enforcement, patrol, collision investigation). When the department installed new computers in 1985, Chief Harry Crum made certain that it would be possible to tabulate law enforcement efforts devoted to specific neighborhoods to answer citizen questions and concerns. As an element of this system, Grand Prairie police officers record codes on arrest reports to reflect the circumstances of the arrest, that is, whether the arrest resulted from a dispatched call, officer’s observation, or traffic enforcement stop. The Grand Prairie PD’s capability to identify arrests made as a consequence of traffic enforcement stops is extremely unusual, and might even be unique among municipal police departments.

RESULTS OF THE REVIEW
Personnel of the Grand Prairie Police Department made a total of 9,566 arrests during 1994. Officers on routine patrols, which included traffic enforcement as an integral part of the department’s overall enforcement program, accounted for 2,868 of those arrests. The special overtime traffic detail made 389 arrests, and an additional 238 arrests were made by traffic personnel at the scenes of collisions. Combined, the three categories of traffic enforcement personnel were responsible for 37 percent of all arrests made by the Grand Prairie Police Department in 1994. Figure 1 illustrates the proportions of all Grand Prairie arrests that were made by traffic and other personnel.
_{Figure 1. Proportions of arrests attributable to traffic and other personnel.}

The contributions of routine traffic patrols, the special overtime detail, and other police personnel to the total number of arrests made in Grand Prairie has remained relatively constant during the past five years, as illustrated by Figure 2. Arrests made by routine traffic personnel have ranged from a high of 2,999 arrests in 1990 to a low of 2,344 in the following year, for an average of 2,700 arrests per year during the five-year period reviewed. Arrests made by the overtime detail, called the Special Traffic Enforcement Program, or STEP, ranged from a low of 164 in 1990 to a high of 399 in 1992, for an average of 305 arrests per year.

A review of 1994 arrest reports revealed that 64 percent of all arrests made by traffic personnel (routine traffic enforcement, STEP, and collision investigators, combined) were made on the basis of outstanding warrants, while 36 percent were non-warrant arrests. Further, slightly more than half of the arrests made by the traffic officers were made for traffic-related offenses, such as warrant arrests for unpaid tickets, and non-warrant arrests for violations of the vehicle code.

More relevant to the current discussion are the 47 percent of all arrests made by Grand Prairie traffic enforcement personnel in 1994 that were for serious and criminal offenses. Serious offenses for which Grand Prairie traffic personnel made arrests in 1994 include 100 arrests for drug violations, 75 arrests for weapons violations, 71 arrests for theft and larceny, 59 arrests for writing bad checks, 53 arrests for assault, 19 arrests for robbery, 17 arrests for burglary, seven arrests for fraud and forgery, and one warrant arrest each for the crimes of kidnapping and murder. In addition, 11 runaway juveniles were taken into custody during the year as a consequence of traffic enforcement stops. The largest category among the serious violations encompasses the alcohol-related offenses, which were responsible for 18 percent of all arrests made by the traffic personnel. Further, 202 arrests were made for outstanding warrants for failing to appear in court, for a variety of reasons. The outstanding warrants account for six percent of all arrests that were made by the traffic personnel.
_{Figure 2. Arrests made by initiating activity.}

Tables 1 and 2 present summaries of the arrests made by Grand Prairie traffic personnel during 1994. Table 1 shows the numbers of warrant and non-warrant arrests that were made by the three types of traffic enforcement activity. Also indicated are the percentages (in parentheses) of warrant and non-warrant arrests by enforcement type.

TABLE 1 WARRANT AND NON-WARRANT ARRESTS MADE BY GRAND PRAIRIE TRAFFIC ENFORCEMENT PERSONNEL IN 1994

Warrant Non-Warrant Total Police Activity Arrests Arrests Arrests
Arrests by Routine Traffic Enforcement 1,887 (66%) 981 (34%) 2,868 Arrests by Overtime Details 276 (71%) 113 (29%) 389 Arrests at Crash Scenes 65 (27%) 173 (63%) 238 Totals 2,228 (64%) 1,267 (34%) 3,495

Table 2 presents the numbers and percentages of traffic-related arrests and arrests made for more serious offenses during the same period. An individual arrest may be characterized by any of the four possible combinations of the two arrest variables, 1) warrant or non-warrant, and 2) traffic-related or serious offense. In other words, an arrest may be made on the basis of an outstanding warrant for either a traffic-related violation (usually an unpaid ticket) or a more serious offense. Conversely, non-warrant arrests may be made for serious offenses discovered by an officer, as well as for traffic-related violations.

TABLE 2 TRAFFIC-RELATED ARRESTS AND ARRESTS FOR OTHER OFFENSES MADE BY GRAND PRAIRIE TRAFFIC ENFORCEMENT PERSONNEL IN 1994

Traffic-Related Arrests for Total Police Activity and Arrests for Other Offenses

Arrests by Routine Traffic Enforcement 1,437 (50%) 1,431 (50%) 2,868 Arrests by Overtime Details 338 (87%) 51 (13%) 389 Arrests at Crash Scenes 71 (30%) 167 (70%) 238 Totals 1,846 (53%) 1,649 (47%) 3,495

Tables 1 and 2 reveal a few differences in the types of arrests that are made by the three categories of traffic enforcement activity. For example, Table 1 shows that routine and overtime patrols made approximately the same proportions of warrant arrests in 1994 (66 and 71 percent respectively), while only 27 percent of the arrests made by officers investigating traffic collisions were warrant arrests. Similarly, Table 2 shows that the routine traffic patrols made equal numbers of arrests for traffic-related and other offenses. In contrast, 87 percent of the arrests made by the overtime patrols were for traffic-related violations, while only 13 percent were for more serious offenses. Also, 70 percent of the arrests made at crash scenes were for serious offenses.

The total number of traffic citations issued by the Grand Prairie Police Department has fluctuated only slightly during the past five years, ranging from a high of 45,009 citations in 1991 to a low of 41,752 in the following year. Although the total number of citations has hovered around the five-year average of 43,447, the relative proportions issued by routine traffic patrols and the STEP details have varied considerably. Figure 3 illustrates the change in numbers of citations issued by routine traffic enforcement and the STEP patrols from 1990 through 1994. The year-to-year variation in numbers of citations issued by the routine and STEP patrols is attributable to changes in deployment strategies and the periodic reallocation of personnel to other responsibilities. For example, both STEP and routine traffic enforcement efforts were reduced during 1994. The traffic enforcement effort was redirected toward youth gang countermeasures; the corresponding declines in the numbers of traffic citations issued in 1994 is depicted in the figure.
_{Figure 3. Numbers of citations issued by STEP and routine traffic enforcement patrols.}

DISCUSSION
The arrest data provided by the Grand Prairie, Texas, Police Department clearly show that traffic enforcement can contribute significantly to the detection of criminal activity and to the apprehension of criminals. Slightly more than half of the arrests (53 percent) made by traffic personnel in 1994 were for traffic-related offenses, primarily driver’s license violations, warrants issued for unpaid traffic citations, and non-warrant arrests for vehicle code violations. Although arresting a driver for no operator’s license and similar offenses might be considered severe treatment by some observers, there is a growing body of evidence that suggests such actions have a positive effect on measures of traffic safety. In particular, unlicensed drivers and drivers who operate without insurance have been found to be disproportionately involved in DWI and hit-and-run crashes in some jurisdictions. Laws that require the arrest of unlicensed and uninsured operators are ways to help reduce the incidence of far more serious traffic offenses.

Perhaps more important than the traffic-related arrests are the 47 percent of the arrests made by Grand Prairie traffic personnel in 1994 that were for serious violations, including DWI, burglary, robbery, and violent crimes. Two hundred violators have been arrested by traffic officers for assaults alone, and nearly 400 on weapons charges in Grand Prairie during the past five years. In addition, 31 runaway juveniles were located by traffic personnel during this period. Most notable, on eight separate occasions between 1990 and 1994, individuals who were wanted for murder were apprehended as a consequence of routine traffic enforcement stops by Grand Prairie officers.

It appears that the large numbers of ancillary arrests made by Grand Prairie PD officers as a consequence of traffic stops are attributable to the specific procedures that are followed. In particular, several years ago Chief Crum implemented a policy requiring officers to make a computer-aided check of the license plate number of each vehicle that is stopped. Further, most officers also use their mobile data terminals to make a computer-aided check of the operator’s license number of drivers who are stopped, automatically checking three state and regional databases for outstanding warrants. Although the original purpose of the procedures was to increase officer safety, the routine checking of license plates and driver’s licenses results in identifying a large number of motorists with outstanding arrest warrants. In 1994, 2,228 arrests were made by Grand Prairie traffic officers in this manner, representing 64 percent of all arrests made as a consequence of traffic enforcement. In addition, 1,267, or 36 percent of the arrests made by traffic officers were made in response to officer observations such as an illegal weapon or contraband in a vehicle.

CONCLUSIONS
The results of the review presented in this brief report document the substantial contributions of Grand Prairie’s traffic enforcement personnel to the detection of illegal activity and the apprehension of criminals. Further, it appears that the Grand Prairie Police Department’s policies that encourage the routine checking of license plate and driver’s license numbers for outstanding warrants, are responsible for the large numbers of both traffic-related and criminal arrests that are made by traffic enforcement personnel.