Lower Crash Rates Research Articles

The association of graduated driver licensing with miles driven and fatal crash rates per miles driven among adolescents

BackgroundGraduated driver licensing (GDL) laws are associated with reduced crash rates per person-year among adolescents. It is unknown whether adolescents crash less per miles driven or drive less under GDL...

Safety Impact of Pavement Conditions

Pavement condition has been known as a key factor related to ride quality, but it is less clear how pavement condition is related to traffic crashes. The researchers used a geographic information system to link data from the Texas Department of Transportation crash record information system and the pavement management information system. Linking the data provided an opportunity to examine in depth the impact of pavement conditions on traffic crashes. This study analyzed the correlation between four key pavement condition scores and crash rates on a large number of crashes on Texas asphalt nonfreeway roadways between 2008 and 2009. The results overwhelmingly suggest that very good pavement conditions coincide with much lower crash rates compared with very poor conditions. The findings of this study provide insights into how pavement conditions might affect crash rates on different types of roadways. The study also provides critical knowledge that may lead to improvements in safety-oriented pavement design. Because of funding shortages, many state roadways suffer severe pavement deterioration, which may result in increased crash rates, as this study suggests. The findings of this study serve as scientific justification for more adequate maintenance of roadways to avoid further safety deterioration. The researchers recommend that state highway agencies maintain fair or good pavement conditions, at a minimum, on all major state highways. When possible, very good pavement conditions should be maintained to reduce crashes.

Do owner–operators pose a safety risk on the nation’s highways?

Despite persistent claims in the motor carrier industry of poorer safety performance of owner–operators, there is little empirical work directly comparing owner–operator safety performance to that of employee drivers. This study assesses the statistical significance of differences in the safety performance between owner–operators and employee drivers. This study also expands on previous driver focused safety models by examining how driver and carrier characteristics affect safety performance. Data for this study were derived from the Motor Carrier Management Information System (MCMIS), and the Commercial Driver’s License Information System (CDLIS) databases. Study results provide evidence that owner–operators are associated with more driver- and vehicle-out-of-service violations but experience lower crash rates than do employee drivers.

Control of Vehicle Braking by Younger and Older Drivers: The Effect of Texture and Size Information

In the current study we examined differences in the use of visual information for the control of braking for older and younger drivers. On each trial, drivers controlled braking in a driving simulator during approach to three stop signs. Their task was to apply smooth and continuous braking and stop in front of the stop signs. The initial time-to contact, initial speed, texture on the ground and size of the stop signs were manipulated. The mean stop distance relative to the stop signs, standard deviation of stop distance, crash rate, mean time-to-contact at onset of braking, and distribution of tau-dot were analyzed. Overall we found that older drivers had larger mean stop distances and lower crash rates as compared to younger drivers. In addition, regulation of tau-dot varied as a function of size for younger but not for older drivers. These results, taken together, suggest that older drivers may use size information differently than younger drivers in braking regulation.

Elderly driving laws and associated crash risk: Analysis of state level data in the USA

Background: There are currently 31 million licensed drivers (or 15% of all licensed drivers) over the age of 65. This number is expected to grow rapidly as the elderly population is predicted to double by 2030. With this impending increase of elderly drivers and their higher susceptibility to physical and mental deterioration, it is important to consider their safety as well as the safety of others on the road. State laws vary significantly as to elderly license renewal periods and renewal requirements, which could be particularly important in assessing elderly drivers’ continued ability to drive. We looked at the duration of license renewal in several states and compared elderly driver crash statistics among states with short and long renewal periods.Methods: 2009 accident data from the NHTSAwas collected and sorted with respect to age and state. Total population estimates, again sorted by age and state, were also collected from the US Census Bureau. The data sets were then compiled to create elderly accident ratios by state and compared to data on license renewal duration (RD). By performing t-tests on data stratified by different RDs, the relationship between state licensing periods and elderly driving characteristics was assessed. Results: When comparing RD to crash rates, only a renewal period of 2 years is associated with lower crash rates (p1⁄4 0.028) among the elderly. The crash rates for these states vary from 55 to 177 crashes per million elderly drivers. The five safest states for elderly drivers (DC, HI,MA, CT, andNY) have variable RDs (2-8 years). The worst 5 states for elderly drivers involved in crashes (MS, AK, MT, KY, and ND) all havemedian license RDs of 4 to 5 years.Conclusions: Frequent renewal (2 years) is associated with a reduction in elderly crashes in our analysis using state level data. However, some of the safest elderly driving states are MA and NY, with 5and 8-year renewal durations respectively. A license renewal period of more than 2 years does not seem to be a efficient predictor of elderly driving crash rates when looking at all 50 states.

Exploring a Bayesian hierarchical approach for developing safety performance functions for a mountainous freeway

While rural freeways generally have lower crash rates, interactions between driver behavior, traffic and geometric characteristics, and adverse weather conditions may increase the crash risk along some freeway sections. This paper examines the safety effects of roadway geometrics on crash occurrence along a freeway section that features mountainous terrain and adverse weather. Starting from preliminary exploration using Poisson models, Bayesian hierarchical models with spatial and random effects were developed to efficiently model the crash frequencies on road segments on the 20-mile freeway section of study. Crash data for 6 years (2000–2005), roadway geometry, traffic characteristics and weather information in addition to the effect of steep slopes and adverse weather of snow and dry seasons, were used in the investigation. Estimation of the model coefficients indicates that roadway geometry is significantly associated with crash risk; segments with steep downgrades were found to drastically increase the crash risk. Moreover, this crash risk could be significantly increased during snow season compared to dry season as a confounding effect between grades and pavement condition. Moreover, sites with higher degree of curvature, wider medians and an increase of the number of lanes appear to be associated with lower crash rate. Finally, a Bayesian ranking technique was implemented to rank the hazard levels of the roadway segments; the results confirmed that segments with steep downgrades are more crash prone along the study section.

Daytime running lights in the USA: what is the impact on vehicle crashes in Minnesota?

BackgroundDaytime running lights (DRLs) are a safety feature intended to reduce crashes by increasing the contrast between vehicles and the background.AimsThe purpose of this study was to determine whether there is an association between vehicles in the USA being equipped with DRLs and crash rates.MethodsThis was a retrospective study using the Minnesota Department of Transportation (MNDOT) Crash Database from 1995 to 2002. Crash reports included in the analyses were limited to accidents involving vehicles 1995 or newer (DRLs not available on prior models) and limited to ideal conditions: (1) daylight, (2) optimal visibility, and (3) dry road surface. The vehicle identification number (VIN) was used to determine the make, model, and year. This information was cross-referenced with a National Highway Traffic Safety Administration table of manufacturer listed DRL conditions to determine vehicle DRL status. Crude crash rates for vehicles were calculated relative to the number of all registered vehicles in Minnesota in 2004, for models 1995–2002. Ninety-five percent confidence intervals (CI) for the rates were constructed assuming a Poisson error distribution.ResultsDuring 1995–2002, there were 184,637 vehicles (1995 or newer) with identifiable VINs involved in accidents which occurred under the specified test conditions. Of these vehicles, 37,909 were determined to have standard DRLs and 146,728 were determined to be models without DRLs (including those listed as DRL optional). The crash rate among vehicles without standard DRLs was 1.73 (95% CI: 1.71–1.75) times higher than the rate for vehicles with standard DRLs. The rate ratio was also significant for fatal vehicle crash rates 1.48 (95% CI: 1.23–1.76).ConclusionMinnesota vehicles equipped with DRLs were associated with a statistically significant lower crash rate compared to vehicles without DRLs from 1995 to 2002.

Using Drivers' Stop/Go Decisions in Driving Simulator to Assess Rear-End Crash Risk at Signalized Intersections

Advanced driving simulators have a potential to be utilized to assess crash risks of driving behaviors, traffic surroundings, and highway designs. This study focused on investigating if drivers' stop/go decisions due to signal change in the simulator's virtual reality can be used to assess rear-end crash risk at the signalized intersection. A signalized intersection with as many important features (including roadway geometries, traffic control devices, intersection surroundings, and buildings) was replicated into a high-fidelity driving simulator. Using the virtual signalized intersection, a driving simulator experiment was conducted to test driver's stop/go decisions at two approaches of the intersection that respectively showed higher and lower rear-end crash risks in the crash history analysis. The experiment results showed that the variability in drivers' stop/go decisions at the higher crash-risk location is higher than that at the lower crash-risk location. Further, through modeling rear-end conflicts based on driver's stop/go probability as a function of potential time to intersection, it was found that the rear-end crash tendency at the two locations displayed by the driver's stop/go behavior in driving simulator is consistent with the finding from the trend in crash history analysis. This research supported that driver's stop/go behavior in a driving simulator can be utilized to assess rear-end crash risk at signalized intersections to seek effective engineering countermeasures to lower crash rates for the high-risk locations.

Incidence and characteristics of school bus crashes and injuries

Objective Studies of school bus crashes have focused on the biomechanics of catastrophic collisions, with very few examining crash incidence. Methods Crashes in the state of Iowa were examined from January 2002 through December 2005. School bus crashes were identified through the Iowa Crash Data, a comprehensive database of all reported crashes in the State of Iowa. School bus mileage data were provided by the Iowa Department of Education. School bus crash, fatality, and injury rates were calculated and differences in crash and injury characteristics between school buses and other vehicles were examined. Results The school bus crash, fatality and non-fatal injury rates were 320.7, 0.4 and 13.6 per 100 million bus miles travelled, respectively. School bus crash fatality and injury rates were 3.5 and 5.4 times lower than overall all vehicle crash fatality and injury rates, respectively. Drivers of other vehicles were more likely to have caused the crash than the bus driver ( P < 0.001). Conclusions School buses experience low crash rates, and the majority of crashes do not lead to injury. Buses are among the safest forms of road transportation, and efforts to educate drivers of other vehicles may help reduce crashes with buses.

A 6-Year Analysis of German Emergency Medical Services Helicopter Crashes

Annually, there are about 80,000 helicopter emergency medical services (HEMS) missions for patients in Germany. In comparison to the commercial transport of passengers, the risk of aviation crashes increases during rescue operations. The aim of this study was to evaluate helicopter crashes related to HEMS in Germany within a 6-year period (1999-2004) and to analyze contributing factors. Flight crashes were identified in the annually published flight crash reports of the Federal Agency for Flight Accident Investigation. Data were completed by telephone interview of the operators and by additional internet information. For statistical analysis, Fisher's exact test was used. A p < 0.05 was considered significant. Twenty-four helicopter crashes (n = 22 during day, n = 2 at night) of German HEMS were identified within the 6 years. Three crashes were fatal, another two caused nonfatal injuries. Seven persons were killed, four injured severely and four slightly. Patients were not hurt within the analyzed period. The crash rate per 10,000 missions sank significantly (p < 0.05), whereas no reduction was found per 100,000 flight hours (not significant) compared with previously published data. Fifty-four percent (n = 13) of all crashes were reported during approach and landing. Seventeen percent (n = 4) of the crashes occurred during ground run and 29% (n = 7) during the remaining flight phases (takeoff and cruise flight). In comparison to previous data a significantly lower crash rate per 10,000 missions was found. With the analysis of the same data per 100,000 flying hours, this trend was not evident. The majority of crashes occurred during the day and landings.

The influence of road curvature on fatal crashes in New Zealand

Bends in roads can cause crashes but a recent study in the UK found that areas with mostly curved roads had lower crash rates than areas with straighter roads. This present study aimed to replicate the previous research in a different country. Variations in the number of fatal road crashes occurring between 1996 and 2005 in 73 territorial local authorities across New Zealand were modelled against possible predictors. The predictors were traffic flow, population counts and characteristics, car use, socio-economic deprivation, climate, altitude and road characteristics including four measures of average road curvature. The best predictors of the number of fatal crashes on urban roads, rural state highways and other rural roads were traffic flow, speed limitation and socio-economic deprivation. Holding significant factors constant, there was no evidence that TLAs with the most curved roads had more crashes than elsewhere. Fatal crashes on urban roads were significantly and negatively related to two measures of road curvature: the ratio of road length to straight distance and the cumulative angle turned per kilometre. Weaker negative associations on rural state highways could have occurred by chance. These results offer limited support to the suggestion that frequently occurring road bends might be protective.

Older drivers, medical condition, medical impairment and crash risk

New evidence has appeared to support the fact that the over-involvement of older drivers in traffic accidents disappears when the low mileage bias is taken into account. As a group, older drivers are as safe as or safer than other age groups, and only low mileage older drivers have a high crash rate. Furthermore, the role of the medical condition of older drivers in traffic accidents, as well as the fitness to drive evaluation, are objects of controversy. We examined all this with a cohort of 4316 drivers attending Medical Driving Test Centres for a mandatory fitness to drive evaluation. Our data shows that older drivers (≥75) have a lower crash rate. Medical conditions that impair fitness to drive, as a tendency, increased with advanced age and with lower mileage group. The multivariate analysis of variance showed that there is an effect ( p < 0.0001) of age-range and mileage on the annual crash rate per million kilometres driven, while a medical restriction (“fit to drive with restriction”) has no effect ( p > 0.05). Our data suggests that health status is not associated with increased crash risk for the low mileage group, although further studies are needed.

Older drivers do not have a high crash risk—A replication of low mileage bias

The widespread claim that older drivers are overly involved in crashes has apparent support from crash data, especially when distance travelled is used as the exposure measure. However, independent of age, drivers travelling more kilometres will typically have lower crash rates per kilometre than those driving fewer kilometres. This paper uses Dutch travel survey data from a large sample of respondents to confirm previous research findings concerning the association between annual mileages driven and crash involvement. When the crash rates of drivers of different ages were compared after being matched for yearly driving distance, most drivers aged 75 years and above were indicatively safer than all other drivers. Only older drivers travelling less than 3000 km per year (just over 10% of all older drivers in the survey) gave any indication of elevated crash rates.

Impact of Infrastructure Characteristics on Road Crashes on Two-Lane Highways

Objective. The main purpose of this study is to estimate and quantify the contribution of the infrastructure to highway crashes and to develop an infrastructure coefficient, that represents the overall characteristics of the highway and could be used as an independent variable in a crash-prediction model. Methods. The infrastructure is defined in this study as the highway and its geometric features, including alignment, road-side elements, sight-distances, presence of guardrails, access-points, roadway consistency, and additional variables that measure the overall quality of the highway alignment and elements. The analysis and developments are conducted for two-lane rural highways. The approach taken is to identify the high crash-rate roads, those with crash rates above 0.25 crashes per million vehicle-km, by Smallest Space Analysis. This type of analysis allows the aggregation of higher crash-rate roads versus lower-crash-rate roads only by their infrastructure coefficients, without consideration of their crash records. Results. Crash rates that are attached by Smallest Space Analysis to the group of roads that had less desirable infrastructure features show a high correlation between the same roads and high crash rates vs. identified better infrastructures and low crash rates. Further analysis shows that low crash-rate infrastructure, as defined in this study for two-lane rural highways, can reduce the crash rate by 44% versus high crash-rate infrastructure, at the 99% confidence level, which is almost a certainty. A model for the prediction of crash rates based on a proposed infrastructure coefficient is calibrated and presented. Conclusions. It is suggested that this model be used in evaluating alternatives for new highways or in improving the alignment and road features of existing highways.

Primary and secondary prevention of drink driving by the use of alcolock device and program: Swedish experiences

To prevent drinking and driving, alcolock (or alcohol-interlock) devices and programs were introduced in Sweden in 1999. Two types of prevention programs were begun. A primary prevention strategy was initiated to prevent alcohol impaired driving by individuals not pre-selected for having prior DWI offences. This approach was first applied as a pilot project in three commercial transport companies (buses, trucks, taxis). Also a secondary prevention trial was begun as a voluntary 2-year program for DWI offenders involving strict medical requirements, including counseling and regular checkups by a medical doctor. The program did not require a prior period of hard suspension and focused on changing alcohol use habits. Alcolocks in commercial vehicles have been well accepted by professional drivers, their employers, and their passengers, and the number of vehicles with alcolocks as a primary prevention measure is rapidly growing in Sweden. Three of 1000 starts in the primary prevention program were blocked by the alcolock after measuring a BAC higher than the legal limit and lock point of 0.02% (20 mg/dl). Only 11% of eligible DWI offenders took part in the voluntary, secondary prevention program. Of these, 60% had diagnoses of alcohol dependence or abuse. During the program, alcohol consumption generally decreased significantly as measured through five biological alcohol markers, and the rate of DWI recidivism fell sharply from a yearly rate of approximately 5% to almost 0. These effects on DWI recidivism are paralleled by reduced rates of police-reported traffic accidents involving injuries and hospital admissions due to road accidents. Successful completion of the program appears to have lasting effects (even 2.5 years later) in terms of far lower rates of DWI recidivism and maybe also lower crash rates. On the other hand those being dismissed from the program appear to rapidly return to previous behaviour. Hard suspension seems almost to have an adverse effect on DWI recidivism, but crashes resulting in injuries may be reduced during revocation.

Taking the Keys from Grandpa

AbstractRecent highly publicized traffic accidents involving older drivers have led to renewed interest in state policies and administrative practices that award and renew drivers’ licenses in the American states. Because the probability of traffic accidents is linked to the medical conditions that are more prevalent among the elderly, and because the number of older drivers is expected to rise over the next several decades, one might expect that this will be an increasingly important policy issue. This article discusses variations that are observed across states in law and administrative practice. A longitudinal analysis of data on crashes involving elderly drivers in fifteen states indicates that crash rates are directly related to the length of the renewal cycle for older drivers and inversely related to the stringency of testing at renewal. It is also likely that states requiring physicians to report conditions that would impair driving will experience lower crash rates. A secondary analysis of policy impacts on the licensing rates is not conclusive, a finding that is attributable to inaccuracies in the reported numbers of licensed drivers.

#58 Age, flight experience and the risk of crash involvement in a cohort of professional pilots

Abstract PURPOSE: Federal Aviation regulations prohibit any individual ages 60 years or older from serving as a pilot on an airplane under Part 121 regulations. The assumption underlying the “Age-60 Rule” is that pilots' safety performance declines with advancing age due to adverse effects of aging on health and cognitive functions. Epidemiological evidence for this premise, however, has been lacking. This study evaluates the risk of crash involvement during the process of aging in a cohort of professional pilots. METHODS: Pilots who were 45–54 years old in 1987 with Class I medical certificates and who flew Part 135 operations (n = 3,306) were followed up for 11 years. Information on demographics, medical conditions, flight experience, crash involvement, and exposure to flight were collected through biannual medical certification data and aviation crash surveillance systems. Proportional hazards modeling was used in the statistical analysis. RESULTS: During the 11-year period, a total of 12,926,214 pilot-flight-hours and 66 crashes were recorded, yielding a crash rate of 0.51 per 100,000 pilot-flight-hours. The crash rates were 0.56, 0.43, 0.55, 1.10 per 100,000 pilot-flight-hours at age 45–49 years, 50–54 years, 55–59 years, 60–64 years, respectively. In the oldest group, the number of crashes was small (n = 3) and some were the result of aircraft malfunction. Pilots with more than 5,000 hours of total flight time at the baseline had significantly lower crash rates than their less experienced counterparts. Multivariate regression revealed that crash risk appeared to increase with age in a quadratic manner; yet the age effect did not reach statistical significance (p = 0.10). CONCLUSION: Safety performance as measured by crash risk in part 135 pilots does not seem to change significantly during the process of aging, possibly due to the “Healthy Worker Effect” resulting from periodic medical certification and voluntary retirement.

Treatment with nasal CPAP decreases automobile accidents in patients with sleep apnea.

We studied 50 consecutive patients to test the hypothesis that successful treatment of obstructive sleep apnea with nasal continuous positive airway pressure (nasal CPAP) will decrease automobile accidents in patients with sleep apnea. Thirty-six (72%) of the patients reported using nasal CPAP regularly during 2 yr. Fourteen patients reported they had not used CPAP during 2 yr. The patients with sleep apnea in this study had a higher automobile crash rate than all drivers in the state of Colorado (0.07 versus 0. 01 crash per driver per year, p < 0.02). Patients who were treated with nasal CPAP had a lower crash rate while being treated than before treatment (0.07 versus 0 crash per driver per year, p < 0.03). Untreated patients with sleep apnea continued to have a high crash rate (0.07 crash per driver before and after diagnosis). Drivers with sleep apnea were reluctant to report their automobile crashes, for the drivers in this study reported only one-third of the crashes in which they were involved. This is the first study to confirm with traffic records that patients with sleep apnea have fewer automobile crashes while being treated with nasal CPAP.

Crash Experience on Tined and Continuously Ground Portland Cement Concrete Pavements

Crash rates were compared between 290 km of continuously ground and 115 km of transversely tined portland cement concrete pavements in Wisconsin. All 11,219 reported crashes at the study sites during the 6-year period 1988 through 1993 were analyzed. Continuously ground surfaces were found to have lower crash rates than tined surfaces under dry and wet conditions during daytime and nighttime as well as under all four combinations of pavement and light conditions. Ground pavements had 58 percent the crash rates of tined pavements under dry and wet conditions; the ratio was 84 percent when snow or ice was present on the pavement; however, relatively limited vehicular travel occurred under such conditions and these results are viewed as preliminary. Ground pavements had 57 percent the crash rates of tined pavements during daytime; the ratio was 73 percent at night. On the basis of the available data, a hypothesis of increasing crash rates with time (based on frictional property deterioration with pavement age, cumulative vehicle passes since construction, or both) could not be confirmed for either type of pavement texture.

Investigation of National Highway System Roadways in the Highway Safety Information System States

Motor vehicle crash rates and roadway characteristics for National Highway System (NHS) and non-NHS roads in seven states—California, Illinois, Maine, Michigan, Minnesota, North Carolina, and Washington— are presented. Accident and roadway data were extracted from the Federal Highway Administration’s Highway Safety Information System. Overall, crash rates on NHS roads were approximately 10 percent lower than those on non-NHS roads, perhaps the result of higher design standards. Crash rates on urban roadways were considerably higher than on the corresponding rural roadways in each state. For rural roadways, fixed-object crash rates were higher on NHS roads than on non-NHS roads. The distribution of crashes by severity was quite similar on NHS and non-NHS roads. For urban freeways, NHS Interstates usually had lower crash rates than NHS non-Interstates. The majority of NHS roads had lane widths of 3.4 m (11 ft) or more, and many had shoulder widths of 1.5 m (5 ft) or more. Compared to NHS non-Interstate roads, NHS Interstate roads were more likely to have lane widths of 3.7 m (12 ft) or over, shoulder widths of 2.4 m (8 ft) or over, paved shoulders, and improved median design. Highway designers and safety officials can use this type of information about accident rates and roadway characteristics to enhance safety by upgrading existing highways and improving the design of NHS highways to some specified roadway design standards and guidelines.