Differences in outcomes of mandatory motorcycle helmet legislation by country income level: A systematic review and meta-analysis.

BACKGROUND: The recent Lancet Commission on Legal Determinants of Global Health argues that governance can provide the framework for achieving sustainable development goals. Even though over 90% of fatal road traffic injuries occur in low- and middle-income countries (LMICs) primarily affecting motorcyclists, the utility of helmet laws outside of high-income settings has not been well characterized. We sought to evaluate the differences in outcomes of mandatory motorcycle helmet legislation and determine whether these varied across country income levels. METHODS AND FINDINGS: A systematic review and meta-analysis were completed using the PRISMA checklist. A search for relevant articles was conducted using the PubMed, Embase, and Web of Science databases from January 1, 1990 to August 8, 2021. Studies were included if they evaluated helmet usage, mortality from motorcycle crash, or traumatic brain injury (TBI) incidence, with and without enactment of a mandatory helmet law as the intervention. The Newcastle-Ottawa Scale (NOS) was used to rate study quality and funnel plots, and Begg's and Egger's tests were used to assess for small study bias. Pooled odds ratios (ORs) and their 95% confidence intervals (CIs) were stratified by high-income countries (HICs) versus LMICs using the random-effects model. Twenty-five articles were included in the final analysis encompassing a total study population of 31,949,418 people. There were 17 retrospective cohort studies, 2 prospective cohort studies, 1 case-control study, and 5 pre-post design studies. There were 16 studies from HICs and 9 from LMICs. The median NOS score was 6 with a range of 4 to 9. All studies demonstrated higher odds of helmet usage after implementation of helmet law; however, the results were statistically significantly greater in HICs (OR: 53.5; 95% CI: 28.4; 100.7) than in LMICs (OR: 4.82; 95% CI: 3.58; 6.49), p-value comparing both strata < 0.0001. There were significantly lower odds of motorcycle fatalities after enactment of helmet legislation (OR: 0.71; 95% CI: 0.61; 0.83) with no significant difference by income classification, p-value: 0.27. Odds of TBI were statistically significantly lower in HICs (OR: 0.61, 95% CI 0.54 to 0.69) than in LMICs (0.79, 95% CI 0.72 to 0.86) after enactment of law (p-value: 0.0001). Limitations of this study include variability in the methodologies and data sources in the studies included in the meta-analysis as well as the lack of available literature from the lowest income countries or from the African WHO region, in which helmet laws are least commonly present. CONCLUSIONS: In this study, we observed that mandatory helmet laws had substantial public health benefits in all income contexts, but some outcomes were diminished in LMIC settings where additional measures such as public education and law enforcement might play critical roles.

Adolescent noncompliance with age-specific versus universal US motorcycle helmet laws: Systematic review and meta-analysis.

INTRODUCTION: The U.S. experience with motorcycle helmets affords an important insight into the responses of adolescents to age-specific laws. Political contention has led to a number of U.S. state law changes back and forth between universal and age-specific laws. Because both kinds of law require adolescent motorcyclists to wear helmets, relatively few studies have focused on how the law type affects their behavior. METHOD: Differential behavior is tested by a systematic review of literature, leading to a meta-analysis, in relation to the experience of various states' motorcycle helmet laws. An electronic search was conducted for before-and-after studies in U.S. states that include data on adolescent helmet usage - both with a universally applicable motorcycle helmet law, and with an age-restricted law (usually, under-21 or under-18) - from observational, injury or fatality records for a certain period (e.g., 12 months) pre and post the state law change. RESULTS: The search yielded ten studies, including two that compared a set of age-specific law states with a set of universal law states over the same time period. Heterogeneity analysis of seven single-state studies with raw data revealed an acceptable fit for a random-effects model. Additional noncompliance with age-restricted laws was indicated by an attributable percentage among exposed of over 65% and odds ratio exceeding 4. CONCLUSIONS: About two-thirds of adolescent noncompliance with age-restricted motorcycle helmet usage laws disappears with universal applicability. Evidence from numerous international studies of youth reaction to helmet laws suggests that a large part of the greater compliance with universal laws is due to their conveying a more convincing message that helmets afford protection against injury. Practical Applications: The meta-analysis provides fresh, young-rider perspective on the continuing debate over motorcycle-helmet laws. Broader insight into adolescent psychology suggests considering alternatives to age-restricted laws more widely in safety and health policy.

Impact of helmet laws on motorcycle crash mortality rates.

BACKGROUND: Helmets are effective in reducing traumatic brain injury. However, population effects of helmet laws have not been well described. This study assesses the impact of helmet laws on the motorcycle (MC) fatality rate in the United States from 1999 to 2015. METHODS: Fatality Analysis Reporting System MC fatalities (aged ≥16 years), crash characteristics, and MC-related laws were collected by year for all 50 states from 1999 to 2015 to create a pooled time series. Generalized linear autoregressive modeling was applied to assess the relative contribution of helmet laws to the MC fatality rate while controlling for other major driver laws and crash characteristics. RESULTS: Universal helmet laws were associated with a 36% to 45% decline in the motorcycle crash mortality rate during the study period across all age cohorts (unstandardized regression coefficients are reported): 16 to 20 years, B = -0.45 (p < 0.05); 21 to 55 years, B = -0.42 (p < 0.001); 56 to 65 years, B = -0.38 (p < 0.04); and older than 65 years, B = -0.36 (p < 0.02). Partial helmet laws were associated with a 1% to 81% increase in the fatality rate compared with states with no helmet laws and a 22% to 45% increase compared with universal laws. Helmet usage did not attenuate the countervailing effect of weaker partial laws for 16 to 20 years (B = 0.01 [p < 0.001]). Other laws associated with a declining motorcycle crash mortality rate included the following: social host/overservice laws, 21 to 55 years (B = -0.38 [p < 0.001]); 56 to 65 years (B = -0.16 [p < 0.002]), and older than 65 years (B = -0.12 [p < 0.003]); laws reducing allowable blood alcohol content, 21 to 55 years (B = -4.9 [p < 0.02]); and laws limiting passengers for new drivers 16 to 20 years (B = -0.06 [p < 0.01]). CONCLUSION: During the period of the study, universal helmet laws were associated with a declining mortality rate, while partial helmet laws were associated with an increasing mortality rate. Other state driver laws were also associated with a declining rate. In addition to universal helmet laws, advocating for strict alcohol control legislation and reevaluation of licenses in older riders could also result in significant reduction in MC-related mortality. LEVEL OF EVIDENCE: Prognostic and epidemiological, level III.

The relationships between correct helmet use, enforcement presence, and mortality in a Latin-America city: The case study of Bogotá, Colombia.

OBJECTIVE: In Bogotá, Colombia, motorcyclists represent a concern as the proportion of motorcycle users between 2013 and 2018 has increased from 18% to 35%. Despite available risk reduction strategies, the fatality rates are also growing, notably in young adults (15-29 years old). This study aims at identifying correct helmet use patterns and its relationship with official records of injuries and casualties in the city over time. METHODS: Between 2015 and 2018, semiannual observational studies of motorcycle users in six randomly selected sites in Bogotá were conducted. Data was collected and analyzed on the number of occupants per vehicle (driver and passengers), gender, approximate age, type of helmet, and whether it was correctly used (strapped) or not. Bivariate and multivariate analyses were performed to identify the determinants of correct helmet use. Additionally, a spatial analysis was conducted to estimate the relationship between motorcycle's casualties and correct use of the helmet (full-face helmet use) prevalence. RESULTS: A total of 77,932 motorcycles were observed, showing a high prevalence of helmet use (99% for drivers and passengers), but only 88% use it correctly (89% drivers and 82% passengers). The presence of enforcement (camera or police personnel) increases the correct use of the helmet, especially in principal roads. Female, adults, and single riders are more likely to correctly wear the helmet. Finally, there is a relationship between the concentration of the fatalities and the incorrect helmet use in 80% of the observational sites. CONCLUSIONS: Incorrect helmet use has been found by the study to be related to higher mortality among motorcycle occupants in Bogotá. Our data shows that enforcement increases correct helmet use with the potential to reduce deaths among motorcycle occupants.

Change in helmet use behavior enforced by CCTV cameras with automatic helmet use detection system on an urban arterial road.

OBJECTIVE: Many developing countries experience a high death toll among motorcycle users (both drivers and passengers), primarily due to a relatively low rate of helmet use resulting from ineffective helmet law enforcement. The objectives of this study are to explore the change in helmet use behavior due to helmet use enforcement by closed-circuit television (CCTV) camera technology with an automatic helmet use detection system and to identify the factors associated with helmet use along an urban arterial road in the city of Khon Kaen, Thailand. METHODS: Data collection was carried out on 49,128 samples by video cameras installed at 5 signalized intersections during 2 periods, namely, before and during the CCTV camera enforcement. The study applied logistic regression analysis to determine factors associated with helmet use and to compare the ratio of helmet use for each variable according to the odds ratio. RESULTS: The study found that CCTV camera enforcement could increase helmet usage at all study intersections by 5.3%. The results imply that 4 factors, including riding status, number of passengers, day of week, and traffic conditions, significantly affected helmet use both before and during the CCTV camera enforcement. Remarkably, 2 more variables, age and police inspection, significantly affected helmet use during the CCTV camera enforcement period. CONCLUSIONS: This study confirms that CCTV camera enforcement can be an important driving force for changing helmet use behavior, particularly for child passengers. Moreover, CCTV camera enforcement can support enforcement by extending coverage to a 24-h period and to intersections without police inspection.

Epidemiology and Pattern of Traumatic Brain Injuries at Annapurna Neurological Institute & Allied Sciences, Kathmandu, Nepal.

BACKGROUND: Traumatic brain injury (TBI) constitutes a major health and socioeconomic problem worldwide. It represents the greatest contribution to death and disability among all trauma-related injuries globally. TBIs are a leading cause of death and disability in Nepal, despite improvements in safety regulations and implementation of strict drunk driving laws. We describe the epidemiology of patients with TBI following admission to our hospital. We discuss the implementation of specific strategies to reduce its incidence. METHODS: We conducted a retrospective cross-sectional study of patients presenting to Annapurna Neurological Institute & Allied Sciences (ANIAS), Kathmandu, with a TBI between September 2018 to September 2019. RESULTS: One-hundred and sixty-seven patients presented with a TBI. The most common age groups were younger than 15 years old and 15-25 years old, and the majority were male (73%). The commonest cause of TBI was road traffic accidents (RTA) (59%). Drivers riding motorcycles were the predominant mechanism of RTA (38%). Helmet use was seen in 57% of patients riding 2-wheelers. Alcohol consumption was reported in 22% of all patients. Skull fractures were the most common diagnosis. Most patients were managed conservatively (84%). CONCLUSIONS: TBI should be recognized as an important public health problem in Nepal. TBI is responsible for a considerable number of neurosurgical admissions to ANIAS. Our study showed patients most vulnerable to TBI are males younger than 25 years old. The implementation of stricter traffic rules and regulations, helmet law enforcement, and public education programs may be helpful in decreasing the number of TBI.

Existing Laws to Combat Road Traffic Injury in Nepal and Bangladesh: A Review on Cross Country Perspective.

BACKGROUND: Road traffic accidents is a leading cause of injury and death globally. The consequences of road traffic accidents are prominent in developing countries that can least afford to meet the health services, economic and societal challenges. Nepal and Bangladesh are two developing country of South Asia who bear a large share of burden due to road traffic injuries. METHODS: A non-systematic review of relevant documents using Google scholar and PubMed as well as review of relevant legal documents was done. RESULTS: Nepal and Bangladesh have traffic laws including all the key risk factors as recommended by the World Health Organization except the child restraint systems laws. The existing laws for both countries include speed, drunk driving, use of seatbelts and motorcycle helmet, driver license, vehicle condition, overloading and accident related compensations.In both the countries for post-crash response, national emergency care access number has partial coverage and in Nepal there are some provisions related to trauma registry.Vulnerable groups are pedestrians with majority of male and higher mortality found in rural areas than urban areas for both the countries. CONCLUSIONS: Both the countries have traffic laws that focus on the prevention of road traffic accidents and protection of victims. However, amendments in the existing laws are required for confronting immediate challenges of increasing accidents and injuries that both the countries face every year.

Using street imagery and crowdsourcing internet marketplaces to measure motorcycle helmet use in Bangkok, Thailand.

INTRODUCTION: The majority of Thailand's road traffic deaths occur on motorised two-wheeled or three-wheeled vehicles. Accurately measuring helmet use is important for the evaluation of new legislation and enforcement. Current methods for estimating helmet use involve roadside observation or surveillance of police and hospital records, both of which are time-consuming and costly. Our objective was to develop a novel method of estimating motorcycle helmet use. METHODS: Using Google Maps, 3000 intersections in Bangkok were selected at random. At each intersection, hyperlinks of four images 90° apart were extracted. These 12 000 images were processed in Amazon Mechanical Turk using crowdsourcing to identify images containing motorcycles. The remaining images were sorted manually to determine helmet use. RESULTS: After processing, 462 unique motorcycle drivers were analysed. The overall helmet wearing rate was 66.7 % (95% CI 62.6 % to 71.0 %). Taxi drivers had higher helmet use, 88.4% (95% CI 78.4% to 94.9%), compared with non-taxi drivers, 62.8% (95% CI 57.9% to 67.6%). Helmet use on non-residential roads, 85.2% (95% CI 78.1 % to 90.7%), was higher compared with residential roads, 58.5% (95% CI 52.8% to 64.1%). Using logistic regression, the odds of a taxi driver wearing a helmet compared with a non-taxi driver was significantly increased 1.490 (p<0.01). The odds of helmet use on non-residential roads as compared with residential roads was also increased at 1.389 (p<0.01). CONCLUSION: This novel method of estimating helmet use has produced results similar to traditional methods. Applying this technology can reduce time and monetary costs and could be used anywhere street imagery is used. Future directions include automating this process through machine learning.

Impacts of helmet law on the changes in potential years of life lost due to traffic injury: a multiple-province evaluation in Vietnam.

INTRODUCTION: This study aimed to evaluate the impact of the helmet law on the changes in potential years of life lost (PYLL) due to traffic mortality and to examine modification effects of socioeconomic factors on the impacts in Vietnam. METHODS: We applied an interrupted time series design using the Bayesian framework to estimate the impact of the law at the provincial level. Then, we used random effects meta-analysis to estimate the impact of the law at the country level and to examine the modification effects of socioeconomic factors. RESULTS: The results indicate that the impacts varied among the provinces. These impacts could be classified by four main groups comprising positive impact, and positive impact without sustainability, possible positive impact, negative or inconsistent impact. For the country-level impact, the results reveal a significantly consistent change in monthly PYLLs at the level of 18 per 100 000 persons, and the post-trend was stable without significant change. The results of meta-regression show that 1 unit increase in the population density (persons/km2), migration rate (%) and income (×1000 dong) are non-significantly associated with increases of PYLLs at 1.3, 27 and 27 per 100 000 person-months, respectively, whereas 1% increase in literacy associated with a decrease of PYLL at 44 per 100 000 person-months. DISCUSSION: Further studies should be warranted to provide a comprehensive evaluation of the law implementation, including its acceptability, adoption, appropriateness, feasibility, cost-effectiveness and sustainability.

Effects of age and violations on occupational accidents among motorcyclists performing food delivery.

BACKGROUND: Risk factors for motorcycle injuries are associated with rider-related factors and crash-related factors. OBJECTIVE: This study investigates the effects of age and violations on occupational accidents among motorcyclists performing food delivery. METHODS: This study analyzed 1,317 injured couriers regarding rider-related factors and crash-related factors according to rider's age or violations. RESULTS: Among injured riders, 67.4% were temporary workers, 76.1% worked in small companies with <5 employees, 58.7% in the nighttime, and 51.5% had a work experience of <1 month. However, among the injured teens, 93.5% were temporary workers, 87.0% in companies with <5 employees, 79.5% in nighttime, and 61.4% with work experience of <1 month. The proportion of novice with <1 month, of the temporary worker, of 'head/face/neck' injury, or of the 'concussion/hemorrhage' type of injury all decreased with age. However, the proportion of 'fracture,' 'rider alone,' or 'death or disability' accidents increased with age. Furthermore, the violation rate was high in teens (17.4%), at night (15.4%), or in type of 'crash with a car' (26.2%). The violation rate decreased with age. CONCLUSIONS: The results are expected to be useful for injury prevention policies and guidelines in the food delivery industries.

When policy meets the pedal: A reduction in motorcyclist fatalities following the implementation of a road traffic law in Lagos, Nigeria.

Objective: The Lagos State Road Traffic Law of 2012 sought to curb reckless okada use and the objective of this study is to determine its impact on motorcyclist fatalities in Nigeria's most densely populated state. This is the first study to date that analyzes the potential impact of the Law on motorcyclist fatalities across Lagos State.Methods: We retrospectively reviewed monthly motorcyclist fatalities in Lagos between January 2012 and December 2015. We analyzed the data using Geographic Information Systems (GIS) software, and used Quantum GIS ver. 2.16.2 to create maps illustrating the spatial-epidemiological distribution of motorcyclist fatalities across Lagos' health facilities. The data was collated into three eight-month periods for analysis (pre-intervention, immediate post-intervention, and sustained post-intervention). Period 1 was January to August 2012, Period 2 was September 2012 to April 2013, and Period 3 was May to December 2013. The data were compared in SPSS using the Welch's ANOVA and Tanhame (post-hoc) tests with a 5% significance level.Results: Motorcyclist fatalities in Lagos fell by an average of 76% over the study period. Over 55% of the fatalities were recorded in five health facilities, located in an area of high road network density. The number of newly registered motorcycles also declined by an average of 69%. The Welch's ANOVA yielded a statistically significant difference between the Periods' means (p < 0.0001). The Tamhane post-hoc test showed significant differences in the mean decrease in fatalities between Period 1 and Period 2 (p = 0.002), and Period 1 and Period 3 (p < 0.0001).Conclusions: This study shows a significant decline in motorcyclist fatalities following the implementation of the Lagos State Road Traffic Law of 2012. A more comprehensive approach to data collection along with an updated law could contribute towards a sustainable reduction of motorcyclist mortality.

Helmet use among motorcycle accident victims in the north-east region of Jamaica.

Currently in Jamaica, motorcyclists account for the largest group of fatalities among all road users. Between 2016 and 2018, a cross sectional study was conducted at the Saint Ann's Bay Regional Hospital involving 155 participants. There were 98.7% males, ages ranged from 14-64 years and more than two thirds of the motorcyclists were under 40 years. Only 29.4% wore helmets, and of those motorcyclists, 52.8% indicated they were only riding for a short distance. Increasing age correlated with increased helmet compliance. Persons with motorcycles greater than 150 cubic centimetres were also more likely to wear a helmet. Interventions to promote increased helmet compliance should take these factors into account in conjunction with enhancing law enforcement.

Scenarios of crashes involving light mopeds on urban bicycle paths.

In the Netherlands, cyclists have to share the bicycle path with light moped riders. These riders are allowed to ride 25 km/h and do not have to wear a helmet (Dutch regulation). Due to several trends such as traffic congestion and the introduction of the scooter model, light mopeds have become more popular, both among older and younger people. This has led to an increased traffic density on bicycle paths as well as concerns about the safety of cyclists. In response to these concerns, several Dutch cities would like to ban light moped riders (LMRs) from the bicycle path and let them ride on the carriageway. However, it is uncertain what the consequences would be for the safety of light moped riders. Moreover, it is not clear to what extent the shared use of bicycle paths leads to serious crashes between cyclists and LMRs. Therefore, an in-depth crash investigation study was carried out to gain more insight into the factors and circumstances that influence the occurrence and consequences of light moped crashes on bicycle paths. A dedicated team for in-depth road crash investigation collected and analyzed detailed information on 36 light moped crashes that occurred on an urban bicycle path. This resulted in a description of the course of events for every crash that was analyzed, including a list of factors that contributed to the occurrence of the crash and possible injuries. Crashes with a similar course of events and a comparable combination of contributory factors were grouped into (sub)types of light moped crashes. Six types of crashes were identified. Based on the contributory crash factors of the identified crash types, remedial measures can be developed to prevent similar crashes from occurring in the future. Moving the LMR to the carriageway is only advisable on 30 km/h roads. Alternative measures to improve the safety of both cyclists and light moped riders include: 1) removing obstacles such as poles from the bicycle path, 2) following guidelines on the minimum width of bicycle paths given traffic volumes, 3) improving sight distances at intersections, 4) traffic light control without conflicts between traffic flows, and 5) introducing a helmet law for light moped riders and their passengers.

Unhelmeted Motorcycle Riders Have Increased Injury Burden: A Need to Revisit Universal Helmet Laws.

BACKGROUND: The aim of this study was to compare hospital outcomes for patients in a motorcycle collision with and without helmet use. The study was conducted as a retrospective analysis of the National Trauma Data Bank's 2013 data set, which included reported data from 100 hospitals across the United States. METHODS: Inclusion criterion for this study is a motorcycle crash involving a driver or passenger. The total number of patients in motorcycle crashes as reported by the National Trauma Data Bank in 2013 was 10,345. Helmet use, hospital stay, ICU and ventilation days, mortality, Glasgow Coma Score, Injury Severity Score, patient payer mix, and complication data were obtained. RESULTS: Patients were divided into two groups: those wearing a helmet (n = 6250) and those without (n = 4095). Patients not wearing a helmet had an increased risk of admission to the ICU (OR = 1.36, P < 0.001, CI 1.25-1.48), requiring ventilation support (OR = 1.55, P < 0.001, CI 1.39-1.72), presenting with a Glasgow Coma Score of eight or below (OR = 2.15, P < 0.001), and in-patient mortality (OR = 2.00, P < 0.001, CI 1.58-2.54). Unhelmeted patients were more likely to have government insurance or be uninsured than those patients wearing a helmet (P < 0.001). CONCLUSIONS: It is not well understood why many states are repealing or have repealed universal helmet laws. Lack of helmet use increases the severity of injury in traumatized patients leading to a substantial financial impact on health care costs. Our analysis suggests the need to revisit the issue regarding laws that require protective headwear while riding motorcycles because of the individual and societal impact. LEVEL OF EVIDENCE: III.

The National Motorcycle Helmet Law at 2 Years: Review of Its Impact on the Epidemiology of Traumatic Brain Injury in a Major Government Hospital in Cambodia.

BACKGROUND: Traumatic brain injury (TBI) is major contributor to the global burden of disease, especially in low- and middle- income countries, where most TBIs are traffic-related. Evidence shows that helmets protect against severe TBI. Cambodia continues to have the greatest motorcycle fatality rate in Southeast Asia. We investigated whether the National Motorcycle Helmet Law introduced in January 2016 had an impact on the epidemiology of motorcycle-related TBI in a neurosurgical referral center in Phnom Penh. METHODS: This is a cross-sectional study of all patients admitted to the Department of Neurosurgery at Preah Kossamak Hospital with TBI following motorcycle accidents between January 2014 and December 2017. RESULTS: TBI admissions increased (from 234 in 2014 to 768 in 2017). The median age was 26 years, and most patients were male. The percentage of helmeted patients was 9% in 2014 and 13% in 2015; this increased to 18% in 2016, but dropped to 9% in 2017. Most TBIs occurred during the evening rush hour. Since 2016, more patients wore helmets in the daytime (up to 23%) than at night (5% between 1:00 and 5:00 am). Skull fracture, the most common pathology pre-law, decreased by 25% post-law (P < 0.001). CONCLUSIONS: With growing urbanization and motorization, TBI is a significant cause of morbidity and mortality in Cambodia. Two years after helmets became compulsory, most patients with TBI are still unhelmeted. Likely contributing factors are low penalty for noncompliance and inconsistent law enforcement. TBI is a major public health problem warranting further efforts to understand how to improve prevention strategies and advocate for change.

Gender and age distribution of motorcycle crashes in Spain.

This study analysed motorcycle crashes in Spain. Ninety-nine thousand three hundred and four motorcycle crash reports filed in the years 2006-2011 were extracted from the Directorate General of Traffic database of crashes with victims. These data were analysed in terms of gender, age groups, trip purpose, type of crash, speed violation, day of the week, harm caused, use of helmet and psychophysical conditions of the driver to study the characteristics of motorcycle crashes in Spain and to assess the differences between male and female motorcycle drivers in these crashes. Significant differences were found in all the variables considered in the study, which implies gender differences in the profile of the injured motorcycle driver. The severity of motorcycle crashes suffered by male drivers is higher than that of women. These results corroborate the need to develop measures differentiated by gender, based on their profile.

A heterogeneity based case-control analysis of motorcyclist's injury crashes: Evidence from motorcycle crash causation study.

The main objective of this study is to quantify how different "policy-sensitive" factors are associated with risk of motorcycle injury crashes, while controlling for rider-specific, psycho-physiological, and other observed/unobserved factors. The analysis utilizes data from a matched case-control design collected through the FHWA's Motorcycle Crash Causation Study. In particular, 351 cases (motorcyclists involved in injury crashes) are analyzed vis-à-vis similarly-at-risk 702 matched controls (motorcyclists not involved in crashes). Unlike traditional conditional estimation of relative risks, the paper presents heterogeneity based statistical analysis that accounts for the possibility of both within and between matched case-control variations. Overall, the correlations between key risk factors and injury crash propensity exhibit significant observed and unobserved heterogeneity. The results of best-fit random parameters logit model with heterogeneity-in-means show that riders with partial helmet coverage (U.S. DOT compliant helmets with partial coverage, least intrusive covering only the top half of the cranium) have a significantly lower risk of injury crash involvement. Lack of motorcycle rider conspicuity captured by dark (red) upper body clothing is associated with significantly higher injury crash risk (odds ratio 3.87, 95% CI: 1.63, 9.61). Importantly, a rider's motorcycle-oriented lower clothing (e.g., cannot easily get stuck in the machinery) significantly lowers the odds of injury crash involvement. Regarding the effectiveness of training, formal motorcycle driving training in recent years was associated with lower injury crash propensity. Finally, riders with less sleep prior to crash/interview exhibited 1.97 times higher odds of crash involvement compared to riders who had more than 5 h of sleep. Methodologically, the conclusion is that the correlations of several rider, exposure, apparel, and riding history related factors with crash risk are not homogeneous and in fact vary in magnitude as well as direction. The study results indicate the need to develop appropriate countermeasures, such as refresher motorcycle training courses, prevention of sleep-deprived/fatigued riding, and riding under the influence of alcohol and drugs.