Number 331 August 2007

Traffic Safety Facts

Traffic Tech – Technology Transfer Series

Preliminary Data Indicate That Booster Seat 

Laws Increase Child Safety Seat Use

U.S. Department of Transportation 1200 New Jersey Avenue SE., Washington, DC 20590

National Highway Traffic Safety Administration

On June 1, 2006, Wisconsin enacted a child passenger safety

law requiring children between 4 and 8 years old or who

weigh between 40 and 79 pounds and are no tallerthan 4 feet

9 inches to be restrained in booster seats. The law does not

require the booster seat to be placed in a back seat. During

a six-month grace period, police issued written warnings

instead of citations for first-time violations. Beginning

January 1, 2007, police issued citations for violations.

Prior to June 1, 2006, Wisconsin law required all children

under 4 to be in child restraints, and children between 4

and 8 years old to be in child restraints or safety belts. While

Wisconsin’s child passenger safety (CPS) law is a primary

enforcement law, meaning police can write tickets to parents

andcaregivers ofimproperly restrainedchildren,Wisconsin’s

adult seat belt law is a secondary enforcement law. Police can

only give an adult seat belt violation if a driver is pulled over

for another violation.

The Wisconsin Department of Transportation developed a

one-page information sheet and card to provide details of the

new law for law enforcement personnel and the public. The

WisconsinBureauofTransportationSafetyalsorananarticleon

the new law in its May newsletter. The American Automobile

Association (AAA) of Wisconsin and Safe Kids Worldwide

(SKW) held a news conference in Madison on June 1 in

conjunction with SKW car seat checks around the State.

In order to examine the effectiveness of this law to increase

booster seat use among children of booster seat age, the

National Highway Traffic Safety Administration contracted

with TransAnalytics, LLC, and its subcontractor, Program

Professionals, Inc., to conduct an observational survey

of booster seat use in Wisconsin before and after the law

changed.

Method

Booster seat observation sites were located in urban and

suburban areas and based on site permission, high numbers

of target vehicles entering the site, safety, and location.

The most common sites were shopping centers with retail

stores that attract the target vehicle group (e.g., Wal-Mart,

Toys“R”Us); elementary schools andchildcare centers;health

care centers; and recreational sites. A convenience sampling

approach was used.

To obtain control/comparison data, booster seat observations

were also conducted in Michigan, a neighboring State that

had no legislative action for enacting a booster seat law.

Under Michigan’s law, all children under the age of 4 must

be in a child restraint system, and children between 4 and

16 must wear a seat belt. All front-seat occupants must wear

seat belts. However, in Michigan, both CPS and seat belt laws

are primary enforcement laws.

Baseline data was collected in the Milwaukee, Wisconsin,

area May 9-11, 2006, and in the Detroit, Michigan, area

May 18-24, 2006. Post-intervention data was collected

in Wisconsin September 6-23, 2006, and in Michigan

September 11 to October 3, 2006.

Data collectors stationed in parking lots and targeted drivers

who were (a) parking their cars; and, (b) transporting at least

one child passenger appearing to be 4 to 8 years old. Upon

receiving the driver’s permission to participate in the study,

data collectors noted the vehicle type, number of passengers,

seating positions, sex, and restraint use.

Results 

Overall,thedriver andvehicle characteristics (e.g.,percentage

of female versus male, race, vehicle types, and number of

occupants) were similar in Wisconsin and Michigan during

the pre- and post-intervention periods.

Although booster seat use among children 4 to 8 years old

increased from 40 to 45.9 percent in Wisconsin and from 38.6

to 40.2 percent in Michigan during this same period, these

increases were not statistically significant (see Table 1).

However, during the pre- and post-booster-seat-law period,

the overall patterns of restraint use (safety belt, child safety

seat [CSS], booster, and unrestrained) for children 4 to 8

changed significantly in Wisconsin (p<.02) and in Michigan

(p<.01). In both States, the number of children in child safety

seats and booster seats increased, and the number of children
TRAFFIC TECH is a publication to disseminate information

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If you would like to receive a copy, contact Patricia Ellison-Potter,

Ph.D., Editor, fax 202-366-7096, e-mail: traffic.tech@dot.gov.

in seat belts decreased. However, in Wisconsin, the number

of unrestrained children remained relatively stable, while the

number in Michigan increased.

Table 1. Restraint Use for Booster-Seat-Age Children

Wisconsin Michigan

Pre 

N=407

Post 

N=355

Pre 

N=472

Post 

N=465

Safety Belt 30.7% 21.1% 45.6% 35.7%

CSS 8.6% 11.8% 3.0% 7.3%

Booster 40.0% 45.9% 38.6% 40.2%

Unrestrained 20.6% 21.1% 12.9% 16.8%

Total 100.0% 100.0% 100.0% 100.0%

Since there is a largevariationinchildren’s sizesbetween4 to8

years old, smaller children would be appropriately restrained

in CSSs with internal harnesses while larger children would

be appropriately restrained in booster seats. There is also

some variation in upper weight limits for forward-facing

CSSs with internal harnesses (e.g., from 40 to 80 pounds), so a

child 40 pounds or over may still be appropriately restrained

in a CSS.

Figure 1. Children Ages 4 to 8 Appropriately Restrained in 

Child Passenger Seats or Booster Seats

40%

45%

50%

55%

60%

Pre Post

Wisconsin Michigan

A chi-square test was performed to determine if there was a

significantdifference from the pre-to post-booster-law period

in the number of children who were appropriately restrained,

without regard to the type of child restraint system. Thus, an

appropriately restrained child could be riding in a booster

seat or in a CSS. In Wisconsin, significantly more children

were appropriately restrained from before to after the law

(p<.02) while the results for Michigan were not significant.

The combination of CSS and booster seat use in Wisconsin

showed an increase of 9.1% (48.6% to 57.7%) and the same

combination yielded an increase in Michigan of 5.9% (41.6%

to 47.5%, see Figure 1).

There was also a trend for children inappropriately restrained

for their age (e.g., in seat belts or completely unrestrained).

In Wisconsin, the number of children in seat belts and the

number of children who were completely unrestrained

decreased 9.1% (51.3% before the law; 42.2% afterthe law). In

Michigan during this same period the number of children in

seat belts and the number of children who were unrestrained

decreased 6% (58.5% before the law; 52.5% after the law).

For bothStates, overhalf ofthe booster seats were the backless

type in the pre- and post-intervention periods.Over one-third

of the booster seats were belt-positioning, high-back models

in the pre- and post-intervention periods. About 10% were

combination seats and only about 2% were shield boosters

in each period.

Conclusions

These findings offer the first indications that Wisconsin’s

Booster Seat Law had the effect of increasing child restraint

system use (CSS or booster seats) for children 4 to 8 years

old. However, this study has limitations because it used a

convenience sample. While not necessarily representative

of the State, the study findings show a significant change in

the direction of safer practices from pre- to post- Wisconsin’s

booster seat law change.

It can be inferred that the booster seat law motivated parents

and caregivers to move their children into some type of

restraint that was appropriate for the child’s age and weight.

Since there was no concomitant change in the comparison

State from pre- to post-intervention (no child booster seat

law was implemented in Michigan), it may be inferred that

the increase in appropriately restrained children inWisconsin

was the result of the new law.

How to Order

The report for Preliminary Data Indicate That Booster 

Seat Laws Increase Child Safety Seat Use prepared by

TransAnalytics, LLC, will be available in the next few months

bywritingtotheOfficeofBehavioralSafetyResearch,NHTSA,

NTI-130, 1200 New JerseyAvenue SE., Washington, DC 20590,

fax 202-366-7096, or download from www.nhtsa.dot.gov. John

Siegler, Ph.D., was the Task Order Manager for this project.

1200 New Jersey Avenue SE., NTI-130

Washington, DC 20590