U.S. Department of Justice

Office of Justice Programs

National Institute of Justice

R e s e a r c h i n B r i e f

National Institute of Justice

Jeremy Travis, Director

continued...

DEPARTMENT OF JUSTICE

OFF ICE OF JUSTICE PROGRAMS

BJA NI J OJJDP BJS OVC

“Designing Out” Gang

Homicides and Street Assaults

November 1998

reducing automobile access to the area,

reduced crime. (For details of the study

method, see “Evaluating Operation Cul

de Sac.”) The study revealed that homicide and aggravated assault fell and that

these crimes were not displaced to other

areas. The tactic used by the LAPD

aimed to help restore the area’s “defensible space.”

The study results are cause for optimism,

but it should be noted that the program

was established and evaluated at one site

only. The same results cannot be guaranteed in other communities, even though

their problems may be similar to those reported here. Thus, jurisdictions that wish

to adopt a program like OCDS should do

so with the realization that further evaluations are needed to confirm the effectiveness of traffic barriers in reducing serious

gang crime.

Gang violence: The product of

opportunity

The underlying assumption of OCDS

was that gang violence, including gangrelated homicide, is partly the result of

criminal opportunity. In this respect the

program directly challenged the popular

notion that gang rivalries are so deepseated, emotionally charged, and irrational that they cannot be mitigated or

The hottest spot for gang-on-gang homicide and assault in the city of Los Angeles had seen gang violence becoming a

cycle of attacks followed by reprisals,

followed by the inevitable counterattacks.

Using a deceptively simple tactic, the Los

Angeles Police Department (LAPD) intervened in an attempt to restore order to the

area. Under the direction of then Assistant Chief of Operations Robert Vernon,

an experiment involving the use of traffic

barriers to block access by automobiles

was launched in 1990 as a means to

“design out” crime by reducing the

opportunities to commit it.

In Operation Cul de Sac (OCDS), as the

program was called, the traffic barriers

were placed in neighborhoods where

gangs and accompanying gang violence

had spiraled out of control. The year

before the project was launched, these

neighborhoods had seen the highest

number of drive-by shootings, gang homicides, and street assaults in the city.

Police intelligence sources indicated that

several street gangs had sold narcotics

and/or engaged in other criminal activity

in the neighborhoods.

In an NIJ-sponsored evaluation, researchers compared crime levels in the OCDS

area before, during, and after its 2 years

of operation to find out if the barriers, by

Issues and Findings

Discussed in this Brief: The use

of a deceptively simple tactic, traffic barriers, to block automobile

access to streets as a way of reducing gang violence. The tactic was

used in a crime-plagued area of

Los Angeles that had experienced

the city’s highest level of drive-by

shootings, gang homicides, and

street assaults. The NIJ-sponsored

evaluation of Operation Cul de Sac

(OCDS), as the program was called,

examined whether the tactic could

reduce gang crime.

Key issues: OCDS was based on the

theory of situational crime prevention, which postulates that crime

occurs partly as the result of opportunity and can be reduced by first

identifying and then blocking these

opportunities rather than attempting

to eliminate “root causes.” The Los

Angeles Police Department noted

that in the OCDS target area gang

crime clustered on the periphery of

neighborhoods linked to major roadways; police set up traffic barriers as

a way to block the opportunities for

crime the roadways created. The

evaluation sought to determine

whether these street closures could

help to “design out” gang crime.

Key findings: In its 2 years of

operation, 1990 and 1991, OCDS

appeared to reduce violent crime.

● The number of homicides and

street assaults fell significantly in

both years and rose after the

program ended.

by James Lasley, California State University, Fullerton
2

R e s e a r c h i n B r i e f

Designing out gang crime

When police and researchers examined

hot spots in the OCDS program area, they

found a systematic pattern of opportunity.

The majority of drive-by shootings and

violent gang encounters occurred in clusters on the periphery of neighborhoods

linked to major thoroughfares. To stem

the violence, the police closed all major

roads leading to and from the identified

hot spots by placing standard cement

K-rails (freeway dividers) at the end of

the streets that led directly to these roads.

This reconfiguration, which essentially

created cul-de-sacs, was completed

within the relatively short period of a

week. Later, the K-rails were replaced

with fixed iron fences which featured a

locked gate that could be opened to permit access by emergency vehicles. Most

of the traffic barrier configurations generally allowed one unrestricted roadway

entrance/exit point.

Violent crime fell significantly

The number of homicides and assaults in

the OCDS area fell significantly during

the 2 years the program was operating,

and rose after it ceased operations, while

in the comparison area the level of these

crimes remained constant.

The year before OCDS began, 1989,

7 homicides were committed in the area.

During the subsequent 2 years—after the

traffic barriers were installed on major

streets in the gang hot spots—only one

homicide was recorded in the OCDS

neighborhood. (See exhibit 1.) The reduction in homicides between the year before

the program began (1989) and the first

year of the program (1990) is statistically

significant and could be the result of

OCDS traffic “design” changes, not random fluctuations in the number of homicides. For assaults, the story is similar.

Between the preprogram year and the

first year, the number of these crimes fell

stopped by specific deterrence measures.

On the contrary, OCDS postulates that

violent gang crime is, in fact, deterrable

because the opportunities, in this case opportunities presented by major roadways

that facilitate entrance to and exit from

high-crime neighborhoods, could be

controlled.

OCDS focused on a proximate cause

rather than a “root cause,” with the goal

of using traffic barriers to decrease the

mobility of rival neighborhood gangs traveling to and from gang crime “hot spots.”

In this way the barriers change the situations in which gangs perceive opportunities to carry out “hit-and-run” crimes

such as drive-by shootings.

Situational crime prevention

One of the leading theories of criminal

opportunity is “situational crime prevention.” Developed by criminologist Ronald

V. Clarke, the theory is based on the assumption that crime can be reduced by

pinpointing and blocking the forces that

facilitate would-be offenders’ criminal

acts.1 Would-be offenders, the theory proposes, make rational choices in planning

their criminal acts. For example, gangs

may choose a particular street to commit

a crime because they rationally determine

that the way the street is situated provides

them with ready access and exit, thereby

creating an opportunity to more easily

elude arrest.

Applying the model to gangs, the LAPD

assumed that they did in fact make a

“rational choice” about whether to engage

in a particular act of criminal violence

and whether to do so in a particular

neighborhood setting. Evidence to support

the theory has come from studies of residential burglary, shoplifting, and other

crimes,2 but OCDS was an initial attempt

to apply situational crime prevention to

gang violence.

● Property crime decreased substantially during the first year of the program but it also decreased in the

comparison area, where there was

no OCDS, indicating that some factor or factors other than the traffic

barriers were responsible for the

reduction in the OCDS site.

● In the second year of the program, property crime rose, suggesting the street closures affected only

violent crime.

● Crime was not displaced to other

areas. Violent crime fell, not only in

the OCDS area, but also in contiguous areas. This may be because the

areas of potential displacement are

the turf of rival gangs. As such they

would be off-limits to gangs that

might want to enter new territory

when the traffic barriers reduced

their opportunities to commit crime

on their own turf.

● Traffic barriers can be used as part

of an approach to maximize neighborhood residents’ defensible space

by increasing their span of control.

Zones configured with the barriers

heighten the visibility of suspect

activities. They can be particularly

effective when combined with

“natural guardians”—people who

serve as informal sources of surveillance and social control.

Although these findings indicate

traffic barriers may work to reduce

violent crime, it should be kept in

mind that the experiment was conducted at only one site. Replications

of OCDS and further evaluations are

needed to fully test the effectiveness

of the tactic.

Target audience: Police chiefs,

sheriffs, urban designers and planners, crime prevention organizations.

Issues and Findings

continued...
3

R e s e a r c h i n B r i e f

Operation Cul de Sac was tested

in a 10-block area (roughly the size of a

census tract) that in 1989 experienced

the highest average number of drive-by

shootings, gang homicides, and street

assaults in the city of Los Angeles. In that

year—the year before the project was

launched—this amounted to approximately 38 drive-by shootings, 7 homicides, and 174 aggravated street

assaults. Police intelligence sources indicated that 25 to 30 hardcore street

gangs (primarily African-American and

Latino/Hispanic street turf-oriented

gangs) had sold narcotics and/or engaged in other criminal activity in the

OCDS test neighborhood.

Comparing crime before and after

OCDS. The researchers used an interrupted quasi-experimental study design,

which measures effects of a program or

other factor before, during, and after

implementation and also compares the

effects to areas that are similar but

where there has been no implementation. Thus, the impact of Operation Cul

de Sac on gang crime was measured by

offenses): homicide, aggravated assault,

and property crime. The homicides and

assaults examined in the study were identified by the LAPD as gang related. The

property crimes examined were burglary,

automobile theft, automobile burglary

(of locked vehicles), grand theft, bicycle

theft, theft from automobiles (from unlocked vehicles), and theft from individuals (larceny).

All crime data were reported by year as

well as quarterly. Because the sample

sizes were very small, tests were conducted to determine their statistical significance,* with the test for significance

set at p< .05. (For findings significant

at this level, the chances are less than 5

in 100 that the result has occurred

randomly.)

* The statistical tests used both parametric

(t-test for correlated samples) and nonparametric methods (the Wilcoxson Matched-Pairs

Test). See Siegel, S., Nonparametric Statistics

for the Behavioral Sciences, New York:

McGraw Hill, 1956.

comparing crime levels in the test area before and after the program began to see if

they fell.

The comparison site. In addition to obtaining and analyzing crime data from the OCDS

site, researchers studied crime in the entire

patrol division surrounding the OCDS site.

The effects of the “experimental” OCDS

program were compared with crime data

from this surrounding comparison area to

detect changes (if any) in the crime level and

to determine the statistical significance of

those changes. The researchers also examined the question of whether crime had

been displaced from the OCDS site to the

comparison area, which is contiguous to the

experimental site.

The program was fully functional from January 1990 to December 1991. The study ran

longer, from 1989 to 1992, to enable researchers to compare crime levels before the

program began and after it ended.

Data sources and reporting. Researchers

used official LAPD data on Part I crimes

(those defined by the FBI as serious

of the barriers opened the roads for

rival gangs from both the OCDS and

comparison areas to freely engage in

drive-by shootings, thereby increasing

the number of homicides in both areas.

This finding may also suggest a “backlash” effect of the traffic closures:

gang rivalries and actions that were

suppressed when the traffic barriers

were installed may have intensified

as a result of the sudden increase in

drive-by shooting opportunities created when the traffic barriers were

removed.

Unlike the situation with homicide,

assault did not increase in the

significantly (from 190 to 163), and

continued to do so the second year

(from 163 to 138). (See exhibit 2.)

Reductions of this magnitude indicate

the change may have been due to the

effects of OCDS.

As predicted by the hypothesis, homicide and assault did not decrease in

the comparison site, where OCDS did

not operate. The numbers remained

static, with no significant decrease

(or increase) in the 2 years of the

program.

Postprogram crime. The year after

the program ceased operations, the

level of homicides and assaults rose in

the OCDS area, as the hypothesis

predicted. Their similarity ends here,

however, because in the comparison

area, where there was no OCDS, the

homicide and assault levels took

different courses.

The statistically significant rise in

homicide in the OCDS area after the

program ended coincided with the

reopening of traffic access to selected

gang hot spots. In the comparison

area a similar statistically significant

increase occurred in this final period,

further supporting the conclusion that

OCDS had suppressed homicides.

The explanation may be that removal

Evaluating Operation Cul de Sac
4

R e s e a r c h i n B r i e f

comparison area after the program

ended in the OCDS. Rather, the level

remained constant.3 One explanation

may be that because aggravated assault is tied to intergang conflict (at

least in the OCDS area), an increase

in this crime in the OCDS area would

come as no surprise. Another possible

explanation is that the traffic closures

reduced the likelihood that gangs

would come into contact with one another (either deliberately or accidentally) in automobiles, and this in turn

reduced the likelihood of assaults until

the barriers were removed.

The barriers did not deter

property crime

Property crime decreased substantially

(approximately 31 percent) during the

first year the traffic barriers were installed. Although it is possible that the

barriers were responsible for reducing

property crime, the study did not provide statistical support for this conclusion. A nearly identical reduction in

property crime took place at the same

time in the comparison area, indicating some other factor was responsible.

During the second year of the program,

property crimes rose to their preprogram levels (about 30 percent, a

statistically significant increase) in the

OCDS area. In the comparison area,

there was a nearly identical increase

(32 percent). Taken together, these

findings suggest that the possible impact of traffic closures on gang-related

crime appears to be limited to violent

offending (homicide and assault). In

fact, it may be that people who committed property crime in the OCDS

area were neighborhood residents

who were unaffected by restrictions in

roadway mobility resulting from the

traffic closures.

Violent crime was not

displaced

One of the central concerns about programs such as OCDS that block the

natural flow of criminal opportunity is

the displacement of criminals and

crime to contiguous neighborhoods.4

No evidence of such a change in

offending patterns was discovered for

the OCDS program. This finding is

contrary to the negative displacement

hypothesis, which holds that gang

members in the OCDS area would

move to contiguous neighborhoods

where they might continue their

violent rivalries under less physically

restrictive conditions.

A possible reason gang-related crime

was not displaced lies in the nature of

gang ties to specific neighborhoods or

turf. The gangs in the OCDS area may

have refrained from committing crime

in surrounding neighborhoods because

these neighborhoods are the turf of

rival gangs. Turfs create natural social

mechanisms that prevent street gangs

from moving at will to new streets,

parks, or blocks. Similarly, rival gangs

traveling by automobile into neighborhoods in the general vicinity of the

OCDS site may have been given the

word to stay clear of the traffic closures, thus avoiding OCDS and contiguous neighborhoods altogether.

Criminals did not adjust their

m.o. to the barriers

There is no reason to believe that

criminals adapted to the OCDS traffic

closures; that is, adjusted their modus

operandi to the closures and used the

barriers to their criminal advantage.

Clearly, if gang members discovered

ways to use the traffic barriers to their

advantage (for example, to avoid the

police or to confront rival gangs), it is

likely that significant increases in violent crime would have occurred by the

second year of OCDS. They did not.

Exhibit 1: Homicides Fell During Operation Cul de Sac

OCDS

BEGINS OCDS ENDS

40

20

4

4 4 4

15

10

5

0

2 3 1 2 3 1 2 3 1 2 3 4

0

1

2

3

35

30

25

Number of Homicides in OCDS Area

1989 1990 1991 1992

Number of Homicides in Comparison Area

OCDS Area Comparison Area

Quarter
5

R e s e a r c h i n B r i e f

Lessons from OCDS

A number of lessons that may be useful in considering the adoption of programs like OCDS can be drawn from

the study findings.

1. Plan traffic flow wisely. Future

attempts to counter gang violence

through traffic closures similar to

those employed in the OCDS program

can be carried out as follows:

● Survey traffic in the target community to identify major flows through

areas that present prime opportunities

for crime (chances are, these areas

will report a large number of crimes,

although, on the other hand, the proportion of unreported crime may be

high). The survey would be conducted

before deciding on the final configuration of the traffic barriers.

● When looking for crime opportunity

areas, try to identify streets, places,

individuals, and objects that may be

considered attractive targets. In addition to gangs and gang hangouts, these

may include liquor stores, fast food

restaurants, schools, parks, parking

lots, poorly lighted locations, and areas where luxury or other cars are not

kept in garages at night. If traffic barriers are included as part of this strategy, it is possible they might be the

factor that works to reduce property

crime at these kinds of targets.

● Configure new traffic patterns.

Channel more traffic into streets that

offer the lowest criminal opportunity:

those that prohibit parking, those

with steady traffic flow that prohibits

stopping, or those bordered by open

areas where the line of vision is unobstructed. The general idea is to use the

new configurations to alter the routines

of offenders who use certain streets on

a regular basis because these routines

mean they cross paths with potential

victims or may come into contact with

their households and their places of

business.

2. Use traffic flow to increase

defensible space. “Defensible

space” refers to physical design that

facilitates neighborhood residents’ tendency to and ability to exercise informal social control. A common strategy

employs mechanisms of access control

to increase the resident-to-outsider

ratio in the hope that residents will

thereby exercise more control over

nonsociable behavior and increase

sociable behavior.5

The ability to restore defensible space

is perhaps the most beneficial crime

prevention feature of traffic barriers.6

For this restoration to occur, the barriers must be used to increase the span

of control of people living in areas

plagued by gang crime. The general

approach is to use barriers to make

suspect activity more visible in neighborhoods that have lost control because vehicle and pedestrian traffic is

unrestricted.

Zones of control can be established

by using traffic barriers to maximize

defensible space. These zones rely on

“natural guardians,” people whose

routine presence in and familiarity

with an area function as the eyes and

ears on the street that ensure a measure of informal social control. If there

are no natural guardians in a traffic

barrier zone, the zone will not deter

crime no matter how skillfully it is

designed. Locations that allow a continuous, unobstructed view of the

zones are the best. In conjunction with

traffic barriers, people who remain at

home during the day (e.g., homemakers, retired people), windows lighted

at night that offer unobstructed views

of the street, and churches or other

gathering places where there is intense activity during the evening and

daytime hours function as natural surveillance mechanisms.

Exhibit 2: Assaults Fell During Operation Cul de Sac

OCDS BEGINS

200

Number of Assaults

1989 1990 1991 1992

190

180

170

160

150

140

130

120

110

100

OCDS Area Comparison Area

196 OCDS ENDS

174 181

163

184

138

187

169
6

R e s e a r c h i n B r i e f

Findings and conclusions of the research reported here are those of the authors and do not

necessarily reflect the official position or policies of the U.S. Department of Justice. James Lasley, Ph.D., teaches in the

Division of Political Science and

Criminal Justice at California State

University, Fullerton. The research

was conducted with support from

NIJ (grant number 96–IJ–CX–

0009). Photocopies of the full report

on which this summary was based,

“Using Traffic Barriers to Design

Out Crime: A Program Evaluation of

LAPD’s Operation Cul de Sac,” are

available at cost from the National

Criminal Justice Reference Service

(NCJRS). The report is also available

through interlibrary loan from NCJRS.

NCJ 173398

The National Institute of Justice is a component

of the Office of Justice Programs, which also

includes the Bureau of Justice Assistance, the

Bureau of Justice Statistics, the Office of

Juvenile Justice and Delinquency Prevention,

and the Office for Victims of Crime.

BULK RATE

U.S. POSTAGE PAID

DOJ/NIJ

Permit No. G–91

U.S. Department of Justice

Office of Justice Programs

National Institute of Justice

Washington, DC 20531

Official Business

Penalty for Private Use $300

3. Foster community involvement. To achieve community acceptance of traffic barrier programs, it is

essential that community members

participate in all phases of program

development. Programs like OCDS

work best in neighborhoods where

citizen patrols or other forms of

community activism against crime

already exist. Traffic closure programs

that embrace the true spirit of community policing—as partnerships in

which responsibilities are shared by

police and the community—can

become effective crime prevention

tools.

Notes

1. Clarke, R.V., “Introduction,” in Situational

Crime Prevention: Successful Case Studies, R.V.

Clarke, ed., New York: Harrow and Heston,

1992.

2. For a study of situational crime prevention

as it relates to residential burglary, see

Cromwell, P., J. Olson, and D. Avary, Breaking

and Entering: An Ethnographic Analysis of

Burglary, Newbury Park, California: Sagel,

1991; for its application to shoplifting, see

Carroll, J., and F. Weaver, “Shoplifters’ Perception of Crime Opportunities: a Processtracing Study,” in The Reasoning Criminal,

D.B. Cornish and R.V. Clarke, eds., New York:

Springer Verlag, 1986. There is a complete

review in Felson, M., Crime and Everyday Life:

Insights and Implications for Society, Thousand

Oaks, California: Pine Forge Press, 1994.

3. Because the reduction in the number of

assaults in the comparison area (from 184 to

169) between 1991—the final year of OCDS—

and 1992 is not a statistically significant

decrease, the number essentially remained

constant.

4. See Clarke, R.V. and D. Weisburd, “Diffusion of Crime Control Benefits: Observations

on the Reverse of Displacement,” in Crime

Prevention Studies, R.V. Clarke, ed., Monsey,

New York: Willow Tree Press, 1994.

5. More research is needed to further support

the concept of defensible space.

6. Newman, O., Creating Defensible Space,

Washington, D.C.: U.S. Department of Housing

and Urban Development, 1996.