Comparison of two methods to assess the effect of age and sex on the risk of car crashes

Background

This study was designed to compare two methods (direct measurement of exposure and quasi-induced exposure) for assessing the effect of age and sex on the risk of being involved in a car crash in Spain.

Methods

Spanish crash rates (per 10,000,000 driver-km) for age and sex groups of drivers aged 18–64 years old were obtained for 2004–2007, using information from the Spanish General Traffic Office (census of reported car crashes) and the Spanish Household Survey on Alcohol and Drugs (estimate of the mean km driven for each car driver). The rate ratios estimated by direct exposure estimates were compared to those obtained with the quasi-induced exposure method, which compares the age and sex of responsible and non-responsible drivers involved in the same clean collision (in which only one of the drivers committed a driving infraction).

Results

Both methods detected an increased risk of involvement in a crash for the youngest (18–20 years) and the oldest drivers (60–64 years), compared to middle-aged drivers (45–49 years). However, the rate ratios obtained with the quasi-induced method for the youngest group (2.0 for men, 1.6 for women) were much lower than those obtained with crash rates (13.4 for men, 5.7 for women). Both methods detected a similar increase in the risk of involvement of male drivers compared to women in the youngest age group. This excess risk for men was maintained with increasing age up to 45–49 years when the quasi-induced method was used. However, direct comparisons of crash rates revealed an increased risk of involvement in women compared to men of the same age from 25–29 years onward.

Conclusions

Both direct measurement of driving exposure and the quasi-induced exposure method detected some well-known patterns of risk associated with driver's age and sex. However, factors that could explain important differences between the two methods deserve attention, especially those related with the excess risk for the youngest drivers as well as sex-related risk.     

Risk factors for causing road crashes involving cyclists: An application of a quasi-induced exposure method

A quasi-induced exposure approach was applied to the Spanish Register of Traffic Crashes to identify driver- and vehicle-related factors associated with the risk of causing a road crash involving a cyclist in Spain from 1993 to 2009. We analyzed 19,007 collisions between a bicycle and another vehicle in which only one of the drivers committed an infraction, and 13,540 records that included the group of non-infractor cyclists in the above collisions plus cyclists involved in single-bicycle crashes. Adjusted odds ratios were calculated for being responsible for each type of crash for each factor considered. Age from 10 to 19 years, male sex, alcohol or drug consumption and non-helmet use were cyclist-related variables associated with a higher risk of crash, whereas cycling more than 1 h increased only the risk of single crashes. Bicycles with brake defects and ridden by two occupants were also at higher risk of involvement in a crash, whereas light defects were associated only with collisions with another vehicle. For drivers of the other vehicle, age more than 60 years, alcohol, not using safety devices and nonprofessional drivers were at higher risk. The risk of colliding with a bicycle was higher for mopeds than for passenger cars.     

Contribution of exposure,risk of crash and fatality to explain age- and sex-related differences in traffic-related cyclist mortality rates

This study was designed to quantify the percent contribution of exposure, risk of collision and fatality rate to the association of age and sex with the mortality rates among cyclists in Spain, and to track the changes in these contributions with time. Data were analyzed for 50,042 cyclists involved in road crashes in Spain from 1993 to 2011, and also for a subset of 13,119 non-infractor cyclists involved in collisions with a vehicle whose driver committed an infraction (used as a proxy sample of all cyclists on the road). We used decomposition and quasi-induced exposure methods to obtain the percent contributions of these three components to the mortality rate ratios for each age and sex group compared to males aged 25–34 years. Death rates increased with age, and the main component of this increase was fatality (around 70%). Among younger cyclists, however, the main component of increased death rates was risk of a collision. Males had higher death rates than females in every age group: this rate increased from 6.4 in the 5–14 year old group to 18.8 in the 65–79 year old group. Exposure, the main component of this increase, ranged between 70% and 90% in all age categories, although the fatality component also contributed to this increase. The contributions of exposure, risk of crash and fatality to cyclist death rates were strongly associated with age and sex. Young male cyclists were a high-risk group because all three components tended to increase their mortality rate.     

An epidemiological study of the risk of cycling in the dark: The role of visual perception,conspicuity and alcohol use

To curtail the rising numbers of cyclists seriously injured in road crashes, more insights are needed into the factors that contribute to these crashes. For instance, darkness is known to be associated with higher injury rates, but little is known about the relative influence of factors such as poor conspicuity, impaired perception and alcohol use among cyclists. To examine these factors, the present study analyzed the epidemiological crash data for three meteorological light conditions: daylight, late evening darkness and early morning darkness; for two crash types: crashes with (M-crashes) and without motorized traffic (NM-crashes); and for different age groups. The relative injury rates (injury risk per distance travelled in darkness corrected for daylight injury risks for each age group) confirmed findings from earlier studies that cycling in late evening darkness is associated with higher injury rates than cycling in daylight conditions. This is the case for both crash types with only small differences between the age groups suggesting that poor conspicuity (M-crashes) and impaired perception (NM-crashes) may play a role. In comparison to late evening darkness, relative injury rates in early morning darkness are much higher. This is the case for both crash types with large differences among the age groups, suggesting that in addition to the absence of daylight also age related risk factors are at play. Support for this hypothesis was found from the analyses of hospital records, showing that the proportion of seriously injured cyclists who have been drinking is highest in early morning darkness and has strongly increased over the last decades. These insights provide input for the selection of countermeasures such as improved lighting (both street and bicycle lights) and interventions targeting alcohol use among cyclists.     

Risk factors for severe injury in cyclists involved in traffic crashes in Victoria,Australia

This study examines the impact of cyclist, road and crash characteristics on the injury severity of cyclists involved in traffic crashes reported to the police in Victoria, Australia between 2004 and 2008. Logistic regression analysis was carried out to identify predictors of severe injury (serious injury and fatality) in cyclist crashes reported to the police. There were 6432 cyclist crashes reported to the police in Victoria between 2004 and 2008 with 2181 (33.9%) resulting in severe injury of the cyclist involved. The multivariate analysis found that factors that increase the risk of severe injury in cyclists involved in traffic crashes were age (50 years and older), not wearing a helmet, riding in the dark on unlit roads, riding on roads zoned 70 km/h or above, on curved sections of the road, in rural locations and being involved in head-on collisions as well as off path crashes, which include losing control of vehicle, and on path crashes which include striking the door of a parked vehicle. While this study did not test effectiveness of preventative measures, policy makers should consider implementation of programs that address these risk factors including helmet programs and environmental modifications such as speed reduction on roads that are frequented by cyclists.     

Fragility versus excessive crash involvement as determinants of high death rates per vehicle-mile of travel among older drivers

Using multiple national data systems, the roles of fragility (susceptibility to injury) versus excessive crash involvement in the increased fatality risk of older drivers per vehicle-mile of travel (VMT) were estimated. For each age and gender group, deaths per driver involved in a crash (a marker of fragility) and drivers involved in crashes per VMT (a marker of excessive crash involvement) were computed. Compared with drivers ages 30-59, those younger than 20 and those 75 or older both had much higher driver death rates per VMT. The highest death rates per mile driven, 13-fold increases, were observed among drivers age 80 or older, who also had the highest death rates per crash. Fragility began to increase at ages 60-64 and increased steadily with advancing age, accounting for about 60-95% of the excess death rates per VMT in older drivers, depending on age group and gender. Among older drivers, marked excesses in crash involvement did not begin until age 75, but explained no more than about 30-45% of the elevated risk in this group of drivers; excessive crashes explained less of the risk among drivers ages 60-74. In contrast, crash over-involvement was the major factor contributing to the high risk of death among drivers younger than 20, accounting for more than 95% of their elevated death rates per VMT. Although both fragility and crash over-involvement contributed to the excess death rates among older drivers per VMT, fragility appeared to be of over-riding importance. These findings suggest that measures to improve the protection of older vehicle occupants in crashes should be vigorously pursued.     

The association of age, sex and helmet use with the risk of death for occupants of two-wheeled motor vehicles involved in traffic crashes in Spain

Background

This study was designed to separate the association of age, sex and helmet use with the risk of death for occupants of two-wheeled motor vehicles (TWMV) involved in crashes into its two theoretical components: severity of the crash and occupant resilience.

Methods

We analyzed the retrospective cohort comprising all 48 016 pairs of drivers and passengers aged 14 years or more in TWMV involved in crashes with victims in Spain from 1993 to 2007 recorded in the Spanish traffic crash registry. The outcome (death or survival), age, sex and helmet use was known for both occupants. Adjusted relative risks (RR) for the association of age, sex and helmet with the risk of death were calculated with Poisson regression models.

Results

Each 1-year increase in age was related with a 3% increase in the risk of death related with lower resilience. The severity-dependent RR of death was 1.84 for male sex and 0.86 for non-helmet use, and the resilience-dependent RR was 0.72 and 2.53, respectively.

Conclusions

The direction and magnitude of the association between age, sex and helmet use and the risk of death of an occupant of a TWMV involved in a crash changed depending on which component of risk was considered: crash severity or occupant resilience. Specifically, female sex and non-helmet use seemed to be associated with crashes of lower severity, but together with increased age they were also related with lower resilience to the energy released in the crash, and therefore with a higher risk of death after adjustment for crash severity. This should be taken into account when assessing the association of individual factors with the risk of death after a crash.     

Pedestrian- and driver-related factors associated with the risk of causing collisions involving pedestrians in Spain

This study aimed to quantify the association between pedestrian- and driver-related factors and the risk of causing road crashes involving pedestrians in urban areas in Spain between 1993 and 2011. From the nationwide police-based registry of road crashes with victims in Spain, we analyzed all 63,205 pairs of pedestrians and drivers involved in crashes in urban areas in which only the pedestrian or only the driver was at fault. Logistic regression models were used to obtain adjusted odds ratios to assess the strength of association between each individual-related variable and the pedestrian’s odds of being at fault for the crash (and conversely, the driver’s odds of not being at fault).The subgroups of road users at high risk of causing a road crash with a pedestrian in urban areas were young and male pedestrians, pedestrians with psychophysical conditions or health problems, the youngest and the oldest drivers, and drivers with markers of high-risk behaviors (alcohol use, nonuse of safety devices, and driving without a valid license). These subgroups should be targeted by preventive strategies intended to decrease the rate of urban road crashes involving pedestrians in Spain.     

Fatal crashes of passenger vehicles before and after adding antilock braking systems

Fatal crash rates of passenger cars and vans were compared for the last model year before four-wheel antilock brakes were introduced and the first model year for which antilock brakes were standard equipment. Vehicles selected for analysis had no other significant design changes between the model years being compared, and the model years with and without antilocks were no more than two years apart. The overall fatal crash rates were similar for the two model years. However, the vehicles with antilocks were significantly more likely to be involved in crashes fatal to their own occupants, particularly single-vehicle crashes. Conversely, antilock vehicles were less likely to be involved in crashes fatal to occupants of other vehicles or nonoccupants (pedestrians, bicyclists). Overall, antilock brakes appear to have had little effect on fatal crash involvement. Further study is needed to better understand why fatality risk has increased for occupants of antilock vehicles.     

An exposure based study of crash and injury rates in a cohort of transport and recreational cyclists in New South Wales,Australia

This paper examines self-reported prospectively collected data from 2038 adult transport and recreational cyclists from New South Wales (Australia) to determine exposure-based incident crash and injury rates. During 25,971 days of cycling, 198 crashes were reported, comprising approximately equal numbers of falls and collisions. The overall crash rate was 0.290 (95% CI, 0.264–0.319) per 1000 km or 6.06 (95% CI, 5.52–6.65) per 1000 h of travel. The rate of crashes causing any injury (self-treated, or medically attended without overnight hospital stay) was 0.148 (95% CI, 0.133–0.164) per 1000 km or 3.09 (95% CI, 2.79-3.43) per 1000 h of travel. The rate of crashes causing a medically attended injury (without overnight hospital stay) was 0.023 (95% CI, 0.020–0.027) per 1000 km or 0.49 (95% CI, 0.43-0.56) per 1000 h of travel. No injuries requiring an overnight stay in hospital were reported on days meeting the inclusion criteria. After adjustment for exposure in hours, or for the risks associated with different infrastructure utilisation, the rates of crashes and medically attended injuries were found to be greater for females than males, less experienced than more experienced cyclists, and for those who rode mainly for transport rather than mainly for recreation. Comparison of estimated crash and injury rates on different infrastructure types were limited by the small number of events, however findings suggest that the separation of cyclists from motorised traffic is by itself not sufficient to ensure safe cycling.     

The influence of passengers on the risk of the driver causing a car collision in Spain. Analysis of collisions from 1990 to 1999

Objective: To determine how the number of passengers, their age and their sex influence the risk of different types of Spanish drivers causing a collision between two or more cars.Methods: We selected, from the Spanish database of traffic crashes resulting in personal injuries or death, those collisions between two or more cars that occurred between 1990 and 1999 in which only one of the involved drivers committed a driving infraction. These drivers were considered the cases; non-infractor drivers were considered their matched controls. We collected information on the number, age and sex of the passengers in each vehicle, along with some potential confounding variables of the drivers and the vehicles involved. Crude and adjusted odds ratios were calculated for the main categories of driver and passenger.Results: A protective effect for the presence of passengers was detected (adjusted odds ratio: 0.69; 95% CI: 0.67-0.70). The protective effect was higher for drivers aged more than 45 years and lower for the youngest drivers (<24 years old). The strongest association was observed for female passengers who accompanied male drivers. The protective effect was lower for passengers older than 64 years.Conclusion: Our results suggest that drivers are less likely to cause a car collision between two or more cars that results in personal injuries or death when they are accompanied by passengers, regardless of driver or passenger characteristics.     

Bicycling crash characteristics: An in-depth crash investigation study

The aim of this study was to describe the crash characteristics and patient outcomes of a sample of patients admitted to hospital following bicycle crashes. Injured cyclists were recruited from the two major trauma services for the state of Victoria, Australia. Enrolled cyclists completed a structured interview, and injury details and patient outcomes were extracted from the Victorian State Trauma Registry (VSTR) and the Victorian Orthopaedic Trauma Outcomes Registry (VOTOR). 186 cyclists consented to participate in the study. Crashes commonly occurred during daylight hours and in clear weather conditions. Two-thirds of crashes occurred on-road (69%) and were a combination of single cyclist-only events (56%) and multi-vehicle crashes (44%). Of the multi-vehicle crashes, a motor vehicle was the most common impact partner (72%) and distinct pre-crash directional interactions were observed between the cyclist and motor vehicle. Nearly a quarter of on-road crashes occurred when the cyclist was in a marked bicycle lane. Of the 31% of crashes that were not on-road, 28 (15%) occurred on bicycle paths and 29 (16%) occurred in other locations. Crashes on bicycle paths commonly occurred on shared bicycle and pedestrian paths (83%) and did not involve another person or vehicle. Other crash locations included mountain bike trails (39%), BMX parks (21%) and footpaths (18%). While differences in impact partners and crash characteristics were observed between crashes occurring on-road, on bicycle paths and in other locations, injury patterns and severity were similar. Most cyclists had returned to work at 6 months post-injury, however only a third of participants reported a complete functional recovery. Further research is required to develop targeted countermeasures to address the risk factors identified in this study.     

Young driver crash rates by licensing age,driving experience,and license phase

Background

Few studies have concurrently assessed the influence of age and experience on young driver crashes, in particular in the post-Graduated Driver Licensing (GDL) era. Further, little attention is given to the transition from intermediate to full licensure. We examined the independent and joint contributions of licensing age, driving experience, and GDL license phase on crash rates among the population of young New Jersey (NJ) drivers.

Methods

From a unique linked database containing licensing and crash data, we selected all drivers who obtained their NJ intermediate license at 17–20 years old from 2006–2009 (n = 410,230). We determined the exact age at which each driver obtained an intermediate and full license and created distinct, fixed cohorts of drivers based on their age at intermediate licensure. For each cohort, we calculated and graphed observed monthly crash rates over the first 24 months of licensure. Further, we examined crash rates by age at licensure, driving experience (i.e., time since licensure), and license phase.

Results

First-month crash rates were higher among the youngest drivers (licensed at 17y0m). Drivers who were licensed later experienced a reduced “steepness” in the slope of their crash rates in the critical initial months of driving, but there did not appear to be any incremental benefit of later licensure once drivers had six months of driving experience. Further, at each age, those with more driving experience had lower crash rates; however, the benefit of increased experience was greatest for the substantial proportion of teens licensed immediately after becoming eligible (at 17y0m). Finally, independent of age and experience, teen drivers’ crash risk increased substantially at the point of transition to a full license, while drivers of a similar age who remained in the intermediate phase continued to experience a decline in crash rates.

Conclusion

Age and driving experience interact to influence crash rates. Further, independent of these two factors, there is an abrupt increase in crash risk at the point of transition from intermediate to full licensure. Future studies should investigate whether this increase is accounted for by a change in driving exposure, driving behaviors, and/or other factors.     

Characteristics of traffic crashes in Maryland (1996-1998): differences among the youngest drivers

Motor vehicle crashes (MVCs) are the leading cause of death among teenagers in the US. The present study examines how crash rates and crash characteristics differed among drivers aged 16-21 in the state of Maryland from 1996 to 1998. The results show that, based on police reports. the youngest drivers have the highest rate of MVCs per licensed driver and per annual miles driven. Furthermore, crash characteristics suggest that inexperience rather than risky driving may account for the differing rates. Drivers closer to the age of 16 had their crashes under the safest conditions: during the day in clear weather while drinking less.     

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.     

Explaining variation in safety performance of roundabouts

The conversion of an intersection into a roundabout has been proven to reduce generally the number of crashes with injuries or fatalities. However, evaluation studies frequently showed considerable individual differences in safety performance of roundabouts or particular groups of roundabouts. The main purpose in the present study was to explain the variance in safety performance of roundabouts through the use of state-of-the-art cross-sectional risk models based on crash data, traffic data and geometric data of a sample of 90 roundabouts in Flanders-Belgium. Poisson and gamma modelling techniques were used, the latter one since underdispersion in the crash data was observed. The results show that the variation in crash rates is relatively small and mainly driven by the traffic exposure. Vulnerable road users are more frequently than expected involved in crashes at roundabouts and roundabouts with cycle lanes are clearly performing worse than roundabouts with cycle paths. Confirmation is found for the existence of a safety in numbers-effect for bicyclists, moped riders and - with less certainty - for pedestrians at roundabouts.     

Overall injury risk to different drivers: combining exposure,frequency, and severity models

Traffic crash risk assessments should incorporate appropriate exposure data. However, existing US nationwide crash data sets, the NASS General Estimates System (GES) and the Fatality Analysis Reporting System (FARS), do not contain information on driver or vehicle exposure. In order to obtain appropriate exposure data, this work estimates vehicle miles driven (VMD) by different drivers using the Nationwide Personal Transportation Survey (NPTS). These results are combined with annual crash rates and injury severity information from the GES for a comprehensive assessment of overall risk to different drivers across vehicle classes.Data are distinguished by driver age, gender, vehicle type, crash type (rollover versus non-rollover), and injury severity. After correcting for drivers' crash exposure, results indicate that young drivers are far more crash prone than other drivers (per VMD) and that drivers of sports utility vehicles (SUVs) and pickups (PUs) are more likely to be involved in rollover crashes than those driving passenger cars. Although, the results suggest that drivers of SUVs are generally much less crash prone than drivers of passenger cars, the rollover propensity of SUVs and the severity of that crash type offset many of the incident benefits for SUV drivers.     

Older driver population and crash involvement trends, 1974-1988.

North Carolina motor vehicle crash data for even-numbered years 1974-1988, inclusive, are analyzed in conjunction with North Carolina population, licensed driver, and mileage data to examine trends in motor vehicle crash involvement by driver age, sex, and race. Crash rates per licensed driver are presented along with crash rates per estimated vehicle miles travelled calculated on the basis of induced exposure. Results focus particularly on older drivers. They show that older drivers' representation in the licensed driver population has increased at a greater rate than their representation in either the census or crash involvement populations. These trends are particularly strong for females and for nonwhites. Furthermore, crash rates have declined more for drivers aged 55 and older than for younger drivers. The greatest declines, both in terms of crashes per licensed driver and crashes per estimated miles travelled, have been experienced by drivers age 65 and older, particularly nonwhites. Males show higher overall crash rates per miles travelled than females, but this effect decreases with age and disappears entirely in the oldest age categories. Results are discussed in light of the changing nature of the overall driving population and the cohort of older drivers in particular.     

Time vs. distance as measures of exposure in driving surveys

A survey of drivers carried out in Ontario in 1988 has provided data on time spent driving as well as the distances driven for licensed drivers of both sexes in six age groups and three regions. Substantial differences were found in times, distances, and distance/time ratios among these groups. Men drove 50% greater distances, but spent only 30% more time driving than women; speed, averaged over each day's driving, was lower for older drivers than for younger drivers. Differences in speed reflect differences in the driving done in urban or rural areas, and differences in the opportunity for road crashes; such differences, whether based on units of time or distance, will also affect both the comparisons of accident rates and the perceptions of risk among different groups of drivers. A definition of exposure to risk of road crash is required that considers both time and distance appropriately.