Nighttime Crashes Research Articles

Roadway Lighting Shows Safety Benefits at Rural Intersections

Intersection-related crashes account for approximately 31% of fatal crashes in Minnesota and roughly 37% of those occurred at night, dusk, or dawn. Nationally, intersection-related fatal crashes accounted for 21% of all fatal crashes and 40% of those crashes occurred during dark, dusk, or dawn light conditions while only 25–33% of the vehicle miles traveled occur at night. Furthermore, Minnesota experienced 70% of its fatal crashes in rural areas, as compared to 58% nationally. As a result, rural intersections at night are at higher risk for fatal crashes than other locations in Minnesota. This research was part of Research Rep. No. MN/RC-2006-35, “Safety impacts of street lighting at isolated rural intersections—Part II.” This research evaluated the effectiveness of roadway lighting in reducing nighttime crashes at isolated rural intersections. A before-and-after study was used to evaluate the impact of lighting at 33 intersections with 3 years of before data and 3 years of after data. A Poisson regressi...

Drinking, Driving, and Crashing: A Traffic-Flow Model of Alcohol-Related Motor Vehicle Accidents

This study examined the influence of on-premise alcohol-outlet densities and of drinking-driver densities on rates of alcohol-related motor vehicle crashes. A traffic-flow model is developed to represent geographic relationships between residential locations of drinking drivers, alcohol outlets, and alcohol-related motor vehicle crashes. Cross-sectional and time-series cross-sectional spatial analyses were performed using data collected from 144 geographic units over 4 years. Data were obtained from archival and survey sources in six communities. Archival data were obtained within community areas and measured activities of either the resident population or persons visiting these communities. These data included local and highway traffic flow, locations of alcohol outlets, population density, network density of the local roadway system, and single-vehicle nighttime (SVN) crashes. Telephone-survey data obtained from residents of the communities were used to estimate the size of the resident drinking and driving population. Cross-sectional analyses showed that effects relating on-premise densities to alcohol-related crashes were moderated by highway trafficflow. Depending on levels of highway traffic flow, 10% greater densities were related to 0% to 150% greater rates of SVN crashes. Time-series cross-sectional analyses showed that changes in the population pool of drinking drivers and on-premise densities interacted to increase SVN crash rates. A simple traffic-flow model can assess the effects of on-premise alcohol-outlet densities and of drinking-driver densities as they vary across communities to produce alcohol-related crashes. Analyses based on these models can usefully guide policy decisions on the sitting of on-premise alcohol outlets.

Evaluation of New Jersey's Graduated Driver Licensing Program

Objective: The objective of this study was to evaluate New Jersey's unique combination of a higher licensing age and a strong GDL system applicable to all novice drivers. Methods: Population-based crash rates for drivers of ages potentially affected by GDL were compared, pre- and post-GDL implementation, with those of adults ages 25–59, using data on fatal crashes and on all police-reported crashes. Results: After GDL implementation, there were statistically significant reductions in the crash rates of 17-year-olds, based on all reported crashes (16%), injury crashes (14%), and fatal crashes (25%), relative to those of drivers ages 25–59. The crash rates of 18-year-olds decreased significantly on the basis of all reported crashes (10%) and injury crashes (10%), relative to those of drivers ages 25–59. The fatal crash involvement rate of 18-year-olds decreased by 4 percent, which was not statistically significant. There was also a statistically significant reduction in fatal crashes of 16-year-old drivers; however, this is unlikely to have been attributable to GDL. Significant reductions in nighttime crashes (of all severity levels) of drivers ages 17 and 18 were observed, as were significant yet smaller reductions in their daytime crash rates. Reductions in fatal crashes of 17- and 18-year-olds carrying more than one passenger were sizable (23 and 24%, respectively) but were not statistically significant. Conclusions: New Jersey's licensing age of 17 eliminates most crashes at age 16. To the extent that the relative inexperience of 17-year-old drivers may negatively impact their crash rates, this effect appears to be largely blunted by New Jersey's strong GDL system. New Jersey's GDL system also reduces crashes at age 18, an age group untouched by other states' GDL systems. New Jersey's combination of licensing policies for young drivers is a model for the nation.

Crash Types: Markers of Increased Risk of Alcohol-Involved Crashes Among Teen Drivers

Teens drink/drive less often than adults but are more likely to crash when they do drink/drive. This study identified alcohol-related crash types for which teen drivers were at greater risk compared with adults. Michigan State Police crash records for drivers ages 16-19 (teens) and 45-65 years (adults) who experienced at least one crash from 1989 to 1996 were used to create alcohol crash types consisting of alcohol-related crashes that included specific combinations of other crash characteristics, such as drinking and driving at night (i.e., alcohol/nighttime). These data were combined with data from the 1990 and 1995 National Personal Travel Surveys and the 2001 National Household Travel Survey to estimate rates and rate ratios of alcohol-related crash types based on person-miles driven. Teens were relatively less likely than adults to be involved in alcohol-related crashes but were significantly more likely to be in alcohol-related crashes that included other crash characteristics. Teen males' crash risk was highest when drinking and driving with a passenger, at night, at night with a passenger, and at night on the weekend, and casualties were more likely to result from alcohol-related nighttime crashes. All the highest risk alcohol-related crash types for teen female drinking drivers involved casualties and were most likely to include speeding, passenger presence, and nighttime driving. The frequency with which passengers, nighttime or weekend driving, and speeding occurred in the highest risk alcohol-related crash types for teens suggests that these characteristics should be targeted by policies, programs, and enforcement to reduce teen alcohol-related crash rates.

Drowsy drivers: The effect of light and circadian rhythm on crash occurrence

Drowsiness has been recognized as a pervasive problem for drivers, with effects comparable to alcohol. Alcohol, however, has a clear legal limit for impairment; there are no comparable criteria to suggest sleepiness. Drowsiness has been associated with light and circadian rhythm. To investigate the joint effects of these factors on crash occurrence, along with other factors, single vehicle crashes reported in Ontario (1999–2004) were analyzed. Crashes occurring at four times of day, when light varies and circadian rhythm is low (2–5 a.m. and 2–4 p.m.) and with similar light conditions and higher circadian rhythm (9–11 p.m. and 10 a.m.–12 noon). Logistic regression was used to see how light and other factors are associated with single vehicle crashes occurring at times of low circadian rhythm, when drowsiness is more likely. Initial results indicated many circumstances associated with occurrence at these times: the age and sex of the driver and reported driver condition as well as weather. There is, however, an interaction between light and presumed alertness. In separate analyses for daytime and night time crashes most variables were significant for nighttime crashes but not for daytime events. The effects of alcohol and youth remained. A lack of light may exacerbate the effects of other factors at times of low alertness; this should be further investigated in controlled environments such as sleep laboratories and/or driving simulators.

How do car crashes happen among young drivers aged 18–20 years? Typical circumstances in relation to license status, alcohol impairment and injury consequences

Aim The study aims to clarify the most typical circumstances in which car crashes involving young drivers and leading to the occurrence of injuries and to consider the various licensing statuses of the drivers in such crashes. Method Young Swedish drivers born between 1984 and 1986 were followed up in the Police register (2003–2004) for their involvement in car crashes as drivers ( n = 2448). A set of five variables (25 categories) descriptive of those crashes was analyzed simultaneously by means of cluster analysis. Associations between crash clusters and licensing status (including none), licensing duration and alcohol involvement were also measured. Results Five clusters were identified, typical of one or some specific crash type(s): single-vehicle in sparsely populated areas, front-on collisions, crashes at dawn or at dusk, turning, cars of later model, crashes in urban areas and speed limits below 50 km/h. Clusters differ in consequences and in the proportions of alcohol impaired drivers involved but not regarding proportions of novice drivers. Unlicensed drivers were found in excess in some clusters (especially single and night time crashes). Conclusion Young drivers are involved in crashes leading to injuries in rather specific circumstances. For some of them, novice drivers or even unlicensed drivers are over-represented, which points to the need for targeted counter-measures, alongside those general ones already in place.

Modeling fault among motorcyclists involved in crashes

Singapore crash statistics from 2001 to 2006 show that the motorcyclist fatality and injury rates per registered vehicle are higher than those of other motor vehicles by 13 and 7 times, respectively. The crash involvement rate of motorcyclists as victims of other road users is also about 43%. The objective of this study is to identify the factors that contribute to the fault of motorcyclists involved in crashes. This is done by using the binary logit model to differentiate between at-fault and not-at-fault cases and the analysis is further categorized by the location of the crashes, i.e., at intersections, on expressways and at non-intersections. A number of explanatory variables representing roadway characteristics, environmental factors, motorcycle descriptions, and rider demographics have been evaluated. Time trend effect shows that not-at-fault crash involvement of motorcyclists has increased with time. The likelihood of night time crashes has also increased for not-at-fault crashes at intersections and expressways. The presence of surveillance cameras is effective in reducing not-at-fault crashes at intersections. Wet-road surfaces increase at-fault crash involvement at non-intersections. At intersections, not-at-fault crash involvement is more likely on single-lane roads or on median lane of multi-lane roads, while on expressways at-fault crash involvement is more likely on the median lane. Roads with higher speed limit have higher at-fault crash involvement and this is also true on expressways. Motorcycles with pillion passengers or with higher engine capacity have higher likelihood of being at-fault in crashes on expressways. Motorcyclists are more likely to be at-fault in collisions involving pedestrians and this effect is higher at night. In multi-vehicle crashes, motorcyclists are more likely to be victims than at-fault. Young and older riders are more likely to be at-fault in crashes than middle-aged group of riders. The findings of this study will help to develop more targeted countermeasures to improve motorcycle safety and more cost-effective safety awareness program in motorcyclist training.

A New Look at NHTSA's Evaluation of the 1984 Charlottesville Sobriety Checkpoint Program: Implications for Current Checkpoint Issues

Objective. Currently, the implementation of sobriety checkpoint programs, which have been demonstrated to be effective in reducing alcohol-related crashes, is limited by the belief that they require large consignments of police officers and result in few arrests. However, one of the earliest evaluations of a checkpoint program in Charlottesville, Virginia, demonstrated that effective checkpoints could be mounted in which police officers made as many arrests as officers on regular patrols. That study was printed by the NHTSA but was not published in a peer-reviewed journal. Because of its significance to current issues in the staffing of and procedures for checkpoint operations, this article reanalyzes the results of that study and describes the procedures implemented in checkpoints. Methods. A before-and-after control design was used to measure the change in nighttime crashes from three baseline years to the program year. Two analyses were conducted: the first on the percentage of all crashes occurring at night in the test city—Charlottesville—and the second on the percentage of all nighttime crashes in the state of Virginia that occurred in the test city. In addition, three waves of random-digit-dialing telephone surveys were conducted: one before and two during the checkpoint program in the test city, and the comparison city, Blacksburg. Finally, the number of impaired-driving arrests per officer hour at the checkpoints was compared with the number of arrests per hour by officers on regular patrol and the effect on arrests of the use of passive sensors was determined. Results. The monthly percentage of nighttime crashes in Charlottesville was reduced by 17% (p = 000) in relation to the baseline level. The percentage of nighttime crashes in the state of Virginia that occurred in Charlottesville was reduced by 11% (p = .013) from baseline levels. Drivers arrested at checkpoints had lower BACs than those arrested by the regular patrols; however, the conviction rates were the same. The arrest per officer hour did not differ significantly between the two types of enforcement operations. Awareness of the checkpoint activity was high (72%) among nighttime at-risk drivers in the test city. Half reported seeing a checkpoint operation, and a quarter reported being interviewed. Use of a passive alcohol sensor by officers at the checkpoint increased arrests by almost a factor of three. Conclusions. The results of the evaluation suggest that small-scale sobriety checkpoints can be implemented as part of the regular enforcement program in moderate-sized jurisdictions and that they can be as efficient in producing arrests as standard enforcement patrols, particularly if passive alcohol sensors are used.

Safety Effectiveness of Selected Treatments at Urban Signalized Intersections

This study conducted a before–after evaluation by means of the empirical Bayes methodology for four types of treatments at signalized intersections with data from Winston-Salem, North Carolina. The results indicated that changing to protected left-turn phasing from permissive or permissive–protected phasing could lead to a virtual elimination of left-turn crashes but other crashes, which were likely to be less severe, could increase. Conversion from nighttime flashback to regular phasing seemed effective in reducing nighttime crashes. Replacing 8-in. signal heads with 12-in. heads seemed effective in reducing right-angle crashes, but this measure could increase other, less-severe crashes. Adding another red-signal lens to an existing one or changing from permissive to permissive–protected left-turn phasing did not seem particularly effective in reducing crashes, but these results were not definitive because they were based on a limited number of sites. Further research using data from other jurisdictions is needed, so that more definitive conclusions can be made about the safety effectiveness of these treatments.

Effects of Age and Illumination on Night Driving: A Road Test

This study investigated the effects of drivers' age and low light on speed, lane keeping, and visual recognition of typical roadway stimuli. Poor visibility, which is exacerbated by age-related changes in vision, is a leading contributor to fatal nighttime crashes. There is little evidence, however, concerning the extent to which drivers recognize and compensate for their visual limitations at night. Young, middle-aged, and elder participants drove on a closed road course in day and night conditions at a "comfortable" speed without speedometer information. During night tests, headlight intensity was varied over a range of 1.5 log units using neutral density filters. Average speed and recognition of road signs decreased significantly as functions of increased age and reduced illumination. Recognition of pedestrians at night was significantly enhanced by retroreflective markings of limb joints as compared with markings of the torso, and this benefit was greater for middle-aged and elder drivers. Lane keeping showed nonlinear effects of lighting, which interacted with task conditions and drivers' lateral bias, indicating that older drivers drove more cautiously in low light. Consistent with the hypothesis that drivers misjudge their visual abilities at night, participants of all age groups failed to compensate fully for diminished visual recognition abilities in low light, although older drivers behaved more cautiously than the younger groups. These findings highlight the importance of educating all road users about the limitations of night vision and provide new evidence that retroreflective markings of the limbs can be of great benefit to pedestrians' safety at night.

Progress in teenage crash risk during the last decade

Objective The purpose of the present study was to examine the most recent data on teenagers' fatal and nonfatal crashes in the United States to determine current crash rates as well as changes in crash rates during the past decade Methods Data for calendar years 1996 and 2005 were extracted for fatal crashes from the Fatality Analysis Reporting System and for police-reported crashes from the National Automotive Sampling System/General Estimates System. To calculate crash rates, population data were obtained from the Census Bureau, and mileage data were obtained from the 2001 National Household Travel Survey Results During 2001–02, the latest year for which mileage data are available, 16 year-old drivers had higher fatal and nonfatal crash rates per mile traveled than all but the very oldest drivers. However, fewer 16 year-olds typically are licensed to drive and they drive fewer miles per year than all but the oldest drivers. Thus, their fatal and nonfatal crash rates per population in 2005 were lower than among other teenagers and among drivers 20–29. During the past decade the most progress has been made in reducing crashes among the youngest drivers. Between 1996 and 2005 both fatal and police-reported crashes per population declined about 40% for 16 year-old drivers, compared with about 25% for 17 year-old drivers and 15–19% for 18 year-old drivers. The greatest reductions for 16 year-olds occurred in nighttime crashes, alcohol-related fatal crashes, and fatal crashes involving multiple teenage passengers. Conclusions Substantial progress has been made in reducing fatal and nonfatal crashes per population among 16 year-old drivers. Although this study was not designed to examine the role of graduated licensing, the results are consistent with the increased presence of such laws, many of which restrict nighttime driving and driving with teenage passengers. Impact on Industry Restrictions on nighttime driving and driving with teenage passengers should be made a part of all states’ graduated licensing systems. Historically, 16 year-olds have had the highest crash risk per licensed driver and per mile traveled. Given the dramatic reductions in per population crash rates among 16 year-olds, it is possible that their per mile and per licensed driver rates also have declined and may no longer be as elevated relative to other ages. However, shortcomings in the licensed driver data and a lack of recent mileage data hamper our ability to examine these issues. If we are to continue to provide a yardstick against which we can measure progress among the youngest drivers, immediate steps need to be taken to restore the availability of reliable exposure data.

Alcohol and other drug use and the transition from riding to driving

Poulin, Boudreau and Ashbridge [Addiction 2007;102(1):51-61.] provide an intriguing analysis of the problem of adolescents riding with drunk drivers. Their analysis, based on a survey of 13 000 students in grades 7-12 in the four Maritime Provinces of Canada, includes individual, school and province variables. Highlighted are the factors not within the student's direct control that determine the extent of riding with a drunk driver (RDD). They found that rural residence, single parent or no parents, socio-economic status (SES), prevalence of driving under the influence (DUI), lower licensure rate and lower educational attainment in the community were associated with RDD. Of particular interest was their finding that, once the impact of those factors was controlled, being licensed reduced the probability of RDD. Presumably, this is because youths with licenses have less need to ride with others and thus are less likely to ride with a drunk driver. The Poulin et al. results highlight the need to pay more attention to the risk that unlicensed youths will become riders in alcohol-related crashes. Sixteen-year-old drivers have crash rates that are three times greater than 17-year-olds and five times greater than 18-year-olds. The current official response to this problem is GDL, which extends the period of adult-supervised driving and provides for an intermediate period when the novice driver may not carry teenage passengers or drive late at night. This should reduce the opportunity for teenage passengers to be injured in crashes involving drinking novice drivers. There is substantial evidence that GDL programs are effective in reducing the crashes of novice drivers. However, there have been no studies of the impact of GDL on teenage passengers. Although imposing night-time restrictions on teenage driversand teenage passengers appears to effectively reduce novice-driver injuries, there is evidence that GDL laws achieve their primary impact through a delay in the licensing of 16- and 17-year-olds. If GDL laws are achieving their impact primarily by limiting the number of licensed 16- and 17-year-olds, then more teenagers in that age group will need rides. It is therefore important to study the limits on mobility (a potential economic burden on some families) and safety (if lack of a license increases RDD) if a teenager is unlicensed. The Poulin et al. paper challenges us to increase our knowledge about RDD as a signal for alcohol problems. It suggests a need to examine more closely the trade-off between discouraging early licensing versus reducing RDD by making licensing more available. It also suggests more research on programs that discourage RDD that go beyond current educational efforts. Language: en

Alcool as the main responsible for recurrent road accidents

The identification of risk factors for recurrent road accidents is the basis for prevention, but very few studies have been published on predictors of recurrence. Our objective was to determine the main variables predicting recurrent crashes in subjects attending an Emergency Department for injuries after road accidents. Over a 5-year follow-up period, we studied 2354 consecutive adult subjects, treated in the Emergency Department following a road accident in 1998. The variables of the original event were tested for predicting recurrence in a Cox proportional hazard model. During follow-up 390/2,325 (16,8%) survivors were treated for injury after a new crash. The overall event rate was 34 per 1000 subject-years. Four variables (age ≤ 32 years, male sex, nighttime crash and blood alcohol concentration > 50 mg/dl) were identified as independent predictors of recurrent crash. After adjustment for sex, age and night-time, alcohol was the leading predictor (relative risk 3,73; 95% confidence interval 3,00-4,64). In the presence of the four variables, the recurrence rate was as high as 145 (117-175) events per 1000 subject-years, and alcohol per se accounted for over 75% of events. In the absence of the four variables, the rate was as low as 11 (7-17) events per 1000 subject-years. Alcohol was the most powerful behavioural factor predicting recurrent events in subjects treated in an Emergency Department for injury after road accidents, along with young age, male gender and night-time. There is a call to action for preventing alcohol on the roads.

Child passenger injury risk in motor vehicle crashes: A comparison of nighttime and daytime driving by teenage and adult drivers

Introduction To examine the association between child passenger injury risk, restraint use, and crash time (day vs. night) for children in crashes of vehicles driven by teenage versus adult drivers. Methods Cross-sectional study involving telephone interviews with insured drivers in a probability sample of 6,184 crashes involving 10,028 children. Results Child passengers in teen nighttime crashes had an increased injury risk and an increased risk of restraint nonuse compared with those in teen daytime crashes. This increased injury risk can be explained by differences in the age of child passengers, collision type, and child passenger's restraint status associated with time of day. Conclusions In order to limit the risk of injury to child passengers driven by teens, Graduated Driver Licensing (GDL) laws should include provisions restricting nighttime driving, as well as mandates for age-appropriate restraint for child passengers. Consideration should also be given for education in child passenger safety for novice teen drivers as part of the licensing process. Impact on Industry Results of this study can be used to support advocacy efforts by the automotive industry and others to promote nighttime driving restrictions on novice drivers. In addition, given that both driver groups were more likely to be involved in a single-vehicle collision during the night, technologies such as electronic stability control may offer opportunities for protection. Further reseach on specific circumstances of teen nighttime crashes is needed to inform industry efforts to improve visibility or vehicle operation under poor lighting conditions.

Trip characteristics of vehicle crashes involving child passengers

Objectives: To describe the trip characteristics of vehicle crashes involving children, and to examine the effect of situational factors on front row seating or inappropriate restraint for young children. Methods:...

A Positive Blood Alcohol Concentration Is the Main Predictor of Recurrent Motor Vehicle Crash

The identification of risk factors for recurrent motor vehicle crashes is the basis for prevention, but few studies have been published on predictors of recurrence. Our objective is to determine the main variables predicting recurrent crashes in subjects attending an emergency department (ED) for injuries after motor vehicle crash. During a 5-year follow-up period, we studied 2,354 consecutive adult subjects treated in the ED after a motor vehicle crash in 1998. The variables of the original event were tested for predicting recurrence in a Cox proportional hazard model. During follow-up, 390 of 2,325 (16.8%) survivors were treated for injury after a new crash. The overall event rate was 34 per 1,000 subject-years. Four variables (age < or =32 years, male sex, nighttime crash, and blood alcohol concentration >50 mg/dL) were identified as independent predictors of recurrent crash. After adjustment for sex, age, and nighttime, alcohol was the leading predictor (relative risk 3.73; 95% confidence interval 3.00 to 4.64). In the presence of the 4 variables, the recurrence rate was as high as 145 (117 to 175) events per 1,000 subject-years, and alcohol per se accounted for more than 75% of events. In the absence of the 4 variables, the rate was as low as 11 (7 to 17) events per 1,000 subject-years. Alcohol was the most powerful behavioral factor predicting recurrent events in subjects treated in an ED for injury after motor vehicle crash, along with young age, male sex, and nighttime.

Probationary and non-probationary drivers' nighttime crashes in Western Australia, 1996–2000

Introduction This study was designed to explore the temporal aspects of crashes for probationary and non-probationary drivers. Methods Data from the West Australian Road Injury Database from 1996–2000 were used to calculate age-sex-specific crash rates per 100,000 person-days and to plot proportions of fatal and hospital crashes by time for probationary and non-probationary drivers. The population attributable risk was used to estimate the potential number of lives saved by nighttime driving restriction in the probationary period. Results Probationary drivers were seven times more likely to crash than non-probationary drivers. While the highest number of crashes was in the daytime, probationary drivers had a higher proportion of fatal or hospitalization crashes at night than non-probationary drivers. Conclusion Restrictions on driving at night could form part of graduated driver training. Even if some probationary drivers disobeyed the restriction, a substantial reduction in car occupant fatalities and hospitalizations could result.

Backseat safety belt use and crash outcome

Low back seat safety belt use has been observed nationally in the United States, but the risk factors for non-use and the effects of non-use on crash outcomes are not well known. This study examined two 2002 New York State public databases: police crash reports and hospital discharge data. Probabilistic linkage applies Bayesian statistical methods to link databases; observed agreements and disagreements of common fields are used to determine the probability of a match. For this study, selected match fields were date and hour of crash, geographic location, gender, age, birthday, name, injury status, crash type, and occupant type. We built a logistic regression model to impute missing values on safety belt use and adjust potentially misclassified values. The backseat occupant safety belt use was adjusted from the recorded 69% to 35% in New York State in 2002. Driver's alcohol involvement, male gender, and nighttime crashes were associated with non-use of safety belts by adult backseat occupants. Non-use of safety belts by backseat passengers was related to higher rates in hospitalization, traumatic brain injury, and vertebral cord injury.

Graduated driver licensing in Utah: Is it effective?

We seek to examine the effectiveness of the graduated driver licensing system in Utah by determining whether crash rates of 16-year-old drivers decreased after graduated driver licensing implementation. We studied 16-year-old-driver crashes using statewide motor vehicle crash data probabilistically linked to emergency department (ED), hospital inpatient, and driver licensure data for 1996 to 2001. Outcomes examined included overall crash rates, nighttime crashes, crash severity indicators (eg, noninjury crash, injury crash, ED crash, inpatient crash, fatal crash), seat belt usage, licensure status, and citations. Rate ratios (RR), chi 2 tests, and interventional time series analyses were used to assess changes before and after graduated driver licensing implementation. There were 27,304 16-year-old-driver crashes during the study period. The overall crash rate per 1,000 licensed 16-year-old drivers decreased by 5% (RR 0.95; 95% confidence interval [CI] 0.92 to 0.97), and a time-series analysis showed a reduction of 0.8 (SD 0.39) crashes per month per 1,000 licensed drivers after graduated driver licensing implementation (1996 to 1999 versus 1999 to 2001). The nighttime crash rate did not change (RR 0.91; 95% CI 0.78 to 1.04), and there was no association between crash severity and graduated driver licensing implementation ( P =.096). Reported seat belt usage increased by 6.3%, and few graduated driver licensing citations were issued by law enforcement. The results suggest that graduated driver licensing may have contributed to a reduction in young driver crashes, but the effects were minimal compared with those shown in many other graduated driver licensing evaluations.

Safety Evaluation of Permanent Raised Snow-Plowable Pavement Markers

Permanent raised pavement markers (PRPMs) often are used to improve preview distances and guidance for drivers in inclement weather and low light conditions. However, studies in three states in the United States have raised concerns about these devices after negative safety effects were found. To address these concerns, an NCHRP project was initiated to assess definitively the safety effects of PRPMs and to develop guidelines for their implementation, by using state-of-the-art methodology and a database from across the United States. This project evaluated the safety performance of snow-plowable PRPMs on two-lane roadways and four-lane freeways by using data collected from five states. The results show that on two-lane roadways selective installations in one state were accompanied by highly significant decreases in total, nighttime, and wet-weather crashes, whereas there was no apparent overall safety benefit for the nonselective installations in two states. A disaggregate analysis of those results found that the nighttime crash effects can be larger on higher-volume roadways and those with degree of curvature of 3.5 or less (radius larger than 500 m). On four-lane freeways, there were some positive indications for wet-weather, guidance-related, and nighttime crashes, with the effects for nighttime crashes increasing as traffic volumes increased. The results of the disaggregate analysis were used to recommend Manual on Uniform Traffic Control Devices guidelines for the implementation of PRPMs.