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

National Highway Traffic Safety Administration

Traffic TECH

Technology Transfer Series

Number 390 July 2010

I

Previous research has found that the proportion of unbelted 

fatalities is greater at night than during the day. Failure to use 

seat belts has been identified as an important factor in nighttime fatalities, yet there are still many gaps in our knowledge 

about seat belt use at night. The primary objective of this 

project was to examine the day and night difference in seat 

belt use under different personal, environmental, and vehicle 

characteristics, in order to identify anomalies that indicate specific traffic safety problems. Differences in day and night use 

in primary and secondary enforcement law States were also 

compared, and an analysis was performed to examine day 

and night seat belt use in States that changed their seat belt 

law from secondary to primary during the 1998-2007 period.

Method

Seat belt use was tracked across years (1998-2007) and across 

States using data from observational surveys of daytime seat 

belt use and the Fatality Analysis Reporting System (FARS). 

Observed daytime belt use rates for States were obtained 

from statewide observational surveys. National seat belt use 

was obtained from NHTSA’s National Occupant Protection 

Use Survey (NOPUS). FARS provided the main measure of 

seat belt use across day and night hours for fatally injured 

passenger vehicle occupants. For the purposes of this analysis, night was defined as 9 p.m. through 3:59 a.m., and day 

was defined as 4 a.m. through 8:59 p.m. Trends in FARS day 

and night belt use were examined for the 10-year period from 

1998 through 2007. Relationships among observed daytime 

seat belt use and FARS daytime and nighttime seat belt use 

were examined, and FARS daytime and nighttime seat belt 

use were compared across gender, age, vehicle type, road 

type, rural/urban areas, driver record, alcohol involvement, 

and primary/secondary law States. 

The Nighttime Problem

For the combined 10-year period, 31% of all the passengervehicle related fatalities took place in crashes that occurred 

during the seven hours identified as nighttime in this study. 

According to the National Household Travel Survey conducted in 2001-2002, only 6.2% of the total daily trips were 

made during these hours. In each of the ten years reviewed, 

seat belt use among fatally injured occupants was lower at 

night than during the day. On average, nighttime seat belt 

use was 18 percentage points lower than daytime belt use. 

Between 1998 and 2007, daytime seat belt use increased 

from 45.8% to 53.5%, an increase of nearly 8 percentage 

points. During the same 10-year period, nighttime seat belt 

use increased from 26.3% to 35.0%, an increase of nearly 9 

percentage points. The figure below illustrates the parallel 

increase in belt use for observed daytime use, daytime use 

by fatally injured occupants, and nighttime use by fatally 

injured occupants.

Trends in Seat Belt Use, 1998-2007

Fatals Day Fatals Night Observed

0%

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

10%

20%

30%

40%

50%

60%

70%

80%

90%

% Belted

Fatals Day = daytime fatally injured front-seat occupants in passenger 

vehicles (FARS). Fatals Night = nighttime fatally injured front-seat occupants in passenger vehicles (FARS). Observed = daytime observed seat 

belt use (NOPUS).

Relationships With Daytime Observational Surveys

Correlations between State daytime observational seat belt use 

rates and seat belt use among fatally injured occupants were 

computed over the 10 years of data. States with high observed 

seat belt use tended to have higher seat belt use rates in fatal 

crashes at all times (day, night, and overall). The correlations 

between observed seat belt use and FARS seat belt use were 

0.67 for nighttime, 0.72 for daytime, and 0.75 overall. 

Targets for Improvement in Nighttime Seat Belt Use

First, daytime and nighttime seat belt use rates for all fatally 

injured outboard front-seat occupants were compared by vari-
TRAFFIC TECH is a publication to disseminate information about 

traffic safety programs, including evaluations, innovative programs, and new publications. Feel free to copy it as you wish. If you 

would like to receive a copy, contact Angela H. Eichelberger, Ph.D., 

Editor, fax 202-366-7394, e-mail: angela.eichelberger@dot.gov.

1200 New Jersey Avenue SE., NTI-132

Washington, DC 20590

ous categories describing gender, age, location of the crash, 

roadway type, and type of vehicle involved. These data were 

based on three years of FARS data (2005 to 2007). The groups 

with low FARS nighttime use were males (31%), those under 

45 years old (33%), SUV/van drivers and passengers (30%), 

secondary law States (26%), rural locations (31%), collector and 

local roads (27%), and lowest of all, pickup truck occupants 

(22%). These categories also showed the lowest daytime use. 

However, the categories that showed the greatest difference 

in FARS belt use from day to night were those 45 and older 

(61% day, 42% night), those on interstate/arterial roads (58% 

day, 41% night), and occupants of cars (59% day, 41% night). 

A second regression analysis was computed for variables 

unique to drivers. Overall FARS seat belt use percentages 

were lowest in drivers who were likely accountable for the 

crash, those with previous suspension(s) or with other previous moving violation(s). Drivers with crashes or violations 

on their records had low FARS belt use during the day (38%) 

and at night (27%). Drivers with clean records had a larger 

disparity in FARS seat belt use from daytime to nighttime 

(53% to 29%). 

FARS Daytime and Nighttime Seat Belt Use by Driver 

BAC, 2003-2007

BAC 

Subgroup*

Day

(4 a.m.–8:59 p.m.)

Night

(9 p.m.–3:59 a.m.)

Day-Night 

Difference

0 59.5% (N=19,454) 52.5% (N=3,618) +7.0

.01 g/dL or above 31.4% (N=6,528) 27.2% (N=8,600) +4.2

.08 or above 27.7% (N=5,349) 26.1% (N=7,855) +1.6

* Based on actual BAC results from States with an average percentage tested of 

at least 80% over the period 1998-2007

A third regression analysis was computed for 28 States that 

reported chemical test results in at least 80% of cases (averaged over 1998-2007) to examine the role of alcohol in daytime and nighttime seat belt use.1

 Seat belt use was compared 

across zero blood alcohol concentration (BAC), any positive 

BAC, and BACs of .08 g/dL or higher. As shown in the table 

below, FARS seat belt use was much higher among zero-BAC 

drivers, both night and day, compared to drivers with positive BACs. This was especially true for drivers with BACs of 

.08 g/dL and higher. The day-night difference was small for 

1 Since time of day is one of the variables used to determine imputed 

alcohol levels in FARS, actual BAC results were used to determine 

alcohol involvement in fatal crashes.

alcohol-impaired drivers (BAC ≥ .08), who had relatively low 

FARS belt use rates both day (27.7%) and night (26.1%).

Effect of Primary Laws on Nighttime Seat Belt Use 

Over the 10-year period, nighttime seat belt use among 

fatally injured occupants was substantially lower than daytime use by an average of nearly 18 percentage points for 

primary States (56.4% day, 38.5% night) and nearly 19 percentage points for secondary States (42.2% day, 23.6% night). 

The impact of changing the seat belt law from secondary to 

primary showed that FARS seat belt use was higher after the 

law than it was prior to the upgrade in law for both daytime 

seat belt use (pre-to-post change of 45.5% to 55.7%) and nighttime seat belt use (pre-to-post change of 26.3% to 37.2%). 

Summary

Study results confirmed that night seat belt use is lower than 

daytime use, but by a much wider margin than has been 

found in previous observational studies. Although there 

were increases over the 10-year period in both daytime and 

nighttime seat belt use, there was a consistent day-night disparity in FARS belt use over the years 1998 to 2007. 

The study results revealed targets for improving nighttime 

seat belt use. Alcohol-impaired drivers are a particularly 

important target because they have illustrated a main reason 

why crash rates are higher during nighttime hours and seat 

belt use lower. Drivers with illegal BACs comprised more 

than two-thirds of fatally injured drivers killed at night, and 

only 26% of these drivers were belted at night. 

The regression analyses allowed a thorough investigation 

of differences in the day/night disparities for various categories. For example, the groups that tended to show the 

greatest gap in belt use from day to night were: occupants 

45 and older, those on interstate roads, car occupants, and 

drivers with clean records. This finding suggests that efforts 

to increase night seat belt use that focus on a broad audience 

that includes both traditionally low-use groups (e.g., pickup 

truck occupants) and relatively high-use groups (e.g., 45 and 

older) might be productive. 

How to Order

To order Daytime and Nighttime Seat Belt Use by Fatally 

Injured Passenger Vehicle Occupants (48 pages), prepared by 

Preusser Research Group, write to the Office of Behavioral 

Safety Research, NHTSA, NTI-130, 1200 New Jersey Avenue 

SE., Washington, DC 20590, fax 202-366-7394, or download 

from www.nhtsa.gov. Angela Eichelberger, Ph.D., was the 

project manager.