J. Richard Stewart

Observed and self-reported seat belt wearing as related to prior traffic accidents and convictions.

During the summer of 1987, 10,000 color-coded mailback questionnaires that identified belted and unbelted North Carolina drivers were handed out at the 72 sites that constitute the probability sample for determining the statewide belt use rate in North Carolina. By obtaining identifying information to determine the winner of a

Evaluation of the effects of North Carolina's 0.08% BAC law

500 prize from among the 5,074 respondents, police-reported traffic accident and conviction records from the North Carolina driver history file were linked to the belted and unbelted respondents. Analyses found that drivers who had been observed not wearing seat belts had 35% more accidents and 69% more convictions than did belted drivers in the previous four-year period. Similar findings were obtained from self-reported belt use.

Evaluating the North Carolina safety belt wearing law

This study was conducted to determine whether the lowered BAC limit for drivers in North Carolina resulted in fewer alcohol-related motor vehicle crashes. We used time-series analysis to examine several indicators of alcohol involvement in both injury and fatal crashes between 1991 and 1996. Data from NC crash files as well as the Fatality Analysis Reporting System (FARS) are used. We also examined several indicators used in previous research on lower BAC limits using a before-after design to compare North Carolina with 37 states that did not change their BAC limit for 24 months before and after the BAC limit was lowered. When controlling for the pre-existing downward trend in drinking driver crashes, along with other pertinent factors such as amount of travel and number of weekends per month, there was no evidence of either a significant shift or a change in the downward trend of alcohol-related crashes associated with the lowered BAC limit. In conclusion, although the lower BAC limit was actively enforced and a substantial proportion of drinkers were aware of the new BAC limit, the drinking-driving population in North Carolina, at the time the lower limit took effect in October 1993, was simply unresponsive to this change.

Bicyclist Intersection Safety Index

The North Carolina Seat Belt Law required an evaluation of the effectiveness of the act with a report of the findings to the Legislature three years after the law went into effect. This paper addresses changes in statewide belt usage and in occupant injury associated with that law. Observational data collected bimonthly from a probability sample of 72 sites stratified by geographic region, rural/urban location, road type, and time of day show that belt use rose from a baseline rate of 25% to a warning ticket phase rate of 45%. Belt use then reached 78% upon enforcement and is now nearly 64%. Time series analysis showed that statistically significant reductions in percentages of moderate and serious injuries occurred at the beginning of both the warning ticket and the enforcement phases. Forecasts of injuries and deaths were also developed from the time series models and were compared with observed totals. Warning tickets brought about a modest 5.4% reduction in serious injuries; fatalities among occupants covered by the law showed no change. In contrast, the subsequent enforcement phase saw a reduction of 11.6% in fatalities and 14.6% in serious or worse injuries. This represents an estimated annual savings of 131 lives and over 2,300 serious injuries in North Carolina during the 18 months following onset of enforcement.

CHANGE IN INJURIES ASSOCIATED WITH SAFETY BELT LAWS

Each year many bicyclists are injured or killed in intersection-related crashes with motor vehicles. The objective of this study was to develop a macrolevel bicycle intersection safety index (Bike ISI) that would allow engineers, planners, and other practitioners to use known intersection characteristics to prioritize intersection approaches with respect to bicycle safety proactively. Using variables that indicate a higher probability of risk for bicyclists, the Bike ISI identifies which intersection approaches have the highest priority for bicycle safety improvements within a particular jurisdiction. Using video data and online ratings surveys, this study obtained data on avoidance maneuvers and safety ratings at 67 intersection approaches and developed a Bike ISI model that incorporated both measures of safety. The Bike ISI uses data on the traffic volume, the number of lanes, the speed limit, the presence of a bike lane, the presence of parking, and the presence of traffic control to give a rating for an intersection approach according to a six-point scale. Using the Bike ISI, practitioners have the ability to evaluate each approach at all intersections in their jurisdictions or at a select group of intersections. Once safety index values are assigned to each site, the practitioner can then select the sites with the highest index values and conduct more detailed reviews of those sites to determine whether any treatments are needed to improve the safety of the intersection.

SEAT BELT USE AND ACCIDENT INVOLVEMENT: A COMPARISON OF DRIVING BEHAVIOR BEFORE AND AFTER A SEAT BELT LAW

Statewide crash data bases from nine states were subjected to time series analyses to detect changes in injuries associated with onset of seat belt laws in the respective states. In each of 18 analyses involving drivers covered by the law observed casualties were below the number forecast on the basis of prior experience and assuming that no law had been enacted. In the case of others, not covered by the law, observed injuries were equally often above or below forecast. Relative to covered drivers not only were the numbers below forecast, but in 12 of the 18 instances there was a statistically significant indication of an abrupt decrease the month the law began.

Index for Assessing Pedestrian Safety at Intersections

In an earlier study, researchers at the University of North Carolina Highway Safety Research Center found drivers classified as seat belt nonusers on the basis of direct observation and self-reported belt use to be overrepresented in prior accidents and violations. This study represents a follow-up and extension of the earlier study where accident and violation rates over a 2.5-year interval following the classification by seat belt use status are compared. Seat belt nonusers were again found to be overrepresented in both accidents and violations. In other analyses of these data, changes in seat belt use status were found not to be associated with changes in accident or violation rates, and seat belt use rates reported by police in accidents following the mandatory seat belt law greatly exceeded both the observed and self-reported use rates. This was especially pronounced for drivers who responded that they rarely or never used seat belts.

The economy as a factor in motor vehicle fatalities, suicides, and homicides

The primary objective of this study was to develop an index that would allow engineers, planners, and other practitioners to prioritize intersection crosswalks with respect to pedestrian safety. The study involved collecting data on pedestrian crashes, conflicts, and avoidance maneuvers as well as subjective ratings of intersection video clips by pedestrian professionals. Sixty-eight pedestrian crosswalks were selected for the pedestrian analysis from Philadelphia, Pennsylvania; San Jose, California; and Miami-Dade County, Florida. A predictive model, the pedestrian intersection safety index (Ped ISI), was developed primarily on the basis of intersection ratings and avoidance maneuvers. Variables in Ped ISI included the number of through lanes, 85th percentile vehicle speed, type of intersection control (signal or stop sign), main street traffic volume, and area type. Through a user-friendly guide, Ped ISI can be used to identify which crosswalks in a city have the highest priority for pedestrian safety i...

ESTIMATING THE EFFECTS OVER TIME OF ALCOHOL ON INJURY SEVERITY

The effect of the economy as reflected by employment and unemployment rates on motor vehicle fatalities, suicides, and homicides is examined using several national databases. First, regression models are fit to these fatality data-overall as well as for a variety of age-race-gender subgroups. Then time series models-autoregressive integrated moving average (ARIMA) and structural time series analysis-were fit to the data, both with and without the economic indicators, to examine the relative ability of the models to forecast subsequent fatalities. No evidence was found using any of the modeling techniques that knowledge of yearly values of rates of employment, unemployment, and nonlabor force leads to improved forecasts of the level of motor vehicle fatalities, suicides, or homicides in the total U.S. population or within various subpopulations of interest.

Cognitive test performance and crash risk in an older driver population

Estimates of the effect of blood alcohol on injury severity obtained through studies of patients at clinical facilities have been found to be quite different from those estimated through the analysis of highway accident data. Several factors have been suggested to account for these differences, including consideration of the relative frequencies of alcohol-involved and alcohol-free drivers who were killed at the scene or who died before reaching a treatment facility. More generally, the nature of the way that the effect of alcohol varies as a function of time from injury may play a important role. In this paper information from highway accident data was combined with time of death information from state medical examiner files to yield estimates of the function P(T), the probability that an injured driver dies at the time T or later from an injury occurring at T = 0, for classes of crash-involved drivers with differing blood alcohol concentrations. Other factors also considered in the analyses included measures of crash severity, driver age, and restraint use. Elevated blood alcohol was consistently found to be associated with shorter survival times.