A National Occupant Protection Use Survey (NOPUS) was conducted in the Fall of 1998 to estimate safety belt and motorcycle helmet use in the U.S. Previous studies were conducted in 1994 and 1996 and the results were made available in a series of research notes.

In 1998, the overall observed safety belt use rate, as measured by NOPUS, was 68.9 percent compared to 61.3 percent observed in 1996 and 58.0 percent observed in 1994. These estimates reflect statistically significant changes in belt use as shown by the 7 percent increase (from 1996 to 1998) and 11 percent increase (from 1994 to 1998).

Background

The 1998 NOPUS was composed of two separate studies: the Moving Traffic Study, which provides information on overall shoulder belt use; and the Controlled Intersection Study, which provides detailed information about shoulder belt use by vehicle type, characteristics of the belt users and child restraint use. This note presents the results from the Moving Traffic Study. Results from the Controlled Intersection Study will be released as the data become available and presented in a research note.

In 1998, the NOPUS separated pickup trucks from the light truck category, thereby creating three categories of vehicle type: passenger cars, pickup trucks, and other passenger vehicles. Other vehicles include vans, minivans, and sport utility vehicles. To compare the results of the 1998 NOPUS to the previous two NOPUS, pickup trucks and other vehicles are combined into the Light Truck category.

Motorcycle helmets that meet the Department of Transportation (DOT) standards are counted as valid protection, whereas those helmets that did not meet DOT standards (considered as substandard) are treated as if the operator/rider were not wearing a helmet.

Data collection from the Moving Traffic Study was conducted at 3,862 sites across the country from September to November 1998. Shoulder belt use was obtained for drivers and right-front passengers only (front outboard seating positions). Three observers were stationed for 30 minutes at interstate/highway exit ramps, controlled (intersections with stop signs or stop lights) and uncontrolled intersections. One observer counted shoulder belt use for the drivers of passenger cars and other vehicles (vans, minivans, and sport utility vehicles (SUVs)). A second observer counted shoulder belt use for the right-front passengers of cars and other vehicles. A third observer counted shoulder belt use for driver and right-front passengers in pickup trucks and helmet use for motorcycle operators and riders. Every day of the week and all daylight hours (8 a.m. to 6 p.m.) were covered by this study. Commercial and emergency vehicles were excluded.

NOPUS was designed as a multi-stage probability sample to ensure that the results would represent occupant protection use in the country. In the first stage, counties were grouped by region (northeast, midwest, south, west), level of urbanization (metropolitan or not), and level of belt use (high, medium, or low). Fifty counties or groups of counties were selected based on the vehicle miles of travel in those locations. In the next stage, a random sample of roadways was selected from two categories: major roads and local roads. Finally, approximately 4,034 intersections or exit ramps were chosen on these roadways. Of the originally selected sites, twenty-two were found to be ineligible during mapping and data collection, while at 150 additional sites no vehicles were observed. A total of 199,412 passenger cars, 135,505 light trucks (of which 76,004 were other vehicles and 59,501 were pickup trucks), and 1,444 motorcycles were observed.

Findings of the 1998 Moving Traffic Study

Detailed results of the moving traffic study are presented in Tables 1 and 2. Each estimate has been statistically weighted according to the sample design. Since these are estimates from a sample, each has an associated margin of error or standard error. Two standard errors are given in parentheses next to each estimate.

By simply adding and subtracting the standard errors from the estimates, approximate 95 percent confidence intervals can be created. This means that one can be 95 percent confident that the true use rate lies within this interval.

Comparison of 1998, 1996 and 1994 Moving Traffic Studies

Collection of the third NOPUS study permits comparisons to be made among similar rates in the 1994, 1996 and 1998 surveys. Table 3 shows these comparisons.

In general, belt use for drivers and passengers of passenger cars and light trucks has increased substantially and are statistically significant compared to 1996. Table 3 shows the largest increases in belt use were in the light truck category.

Overall helmet use rates for motorcyclists in 1998 increased by 3.1 percent compared to 1996, slightly higher than the increase seen between 1996 and 1994. However, when motorcycle operators are separated from riders, the data show a continuing trend downward in the motorcycle operators' use of helmets from 1994 to 1998. Conversely, motorcycle riders' use of helmets increased dramatically in 1998 when compared to the previous two NOPUS. Only one state in the NOPUS relaxed their helmet use law since the 1996 NOPUS; the other states in the survey have had no changes since 1992.

Findings of the 1998 State Surveys

The National Highway Traffic Safety Administration (NHTSA) also obtains belt use rates from each of the 50 states and the District of Columbia. In 1998, the national belt use rate, based on individual state surveys, was 68.7 percent. To calculate this number, the belt use rates from each state's most recent survey is weighted by that state's proportion of the total U.S. population.

State safety belt surveys differ in design even though most states now conduct probability-based observational surveys. The state survey designs may differ in the following ways: (1) all states include major roads, while only a portion of the states include local roads, (2) some states include the entire state in the survey design, while other states exclude areas that account for less than 15 percent of the state's population, (3) the majority of states had an adequate number of observation sites, while the remaining states used what was cost effective, and (4) different estimation procedures.

Comparison of Measurement Methods

The findings of the 1998 NOPUS are not inconsistent with the national use rate estimates as calculated from state surveys.

Direct comparison of findings between the NOPUS and state surveys is difficult, primarily because of the differences in the methodology the states used to collect the belt use data. However, a rough comparison of overall use can be made between the state-based estimate of 68.7 percent and the NOPUS estimate of 68.9 percent. In this comparison, the state-based estimate falls within the 95 percent confidence interval of the NOPUS estimate.

State surveys provide an essential source of information for monitoring progress in the states. The NOPUS provides a probability-based sample of national use with the ability to estimate sampling variability. In addition, the NOPUS provides a unique source of detailed information concerning restraint use by vehicle type, age, gender, shoulder belt misuse, etc. Plans for repeating the NOPUS survey will be based upon the frequency of need for this level of analysis and budgetary considerations. Annual estimates of belt use progress will continue to be made with the state-based surveys.

For additional copies of this research note, please call (202) 366-4198 or fax your request to (202) 366-7078. For questions regarding the data reported in this research, contact Nancy Bondy [202-366-5353] or Dennis Utter [202-366-5351] of the National Center for Statistics and Analysis. This research note and other general information on highway traffic safety may be accessed by Internet users at http://www.nhtsa.dot.gov/people/ncsa.