Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Conclusions 11.1 Research Findings Motorcycle riders now account for more fatalities than the passengers of any other vehicle type involved in a guardrail collision. In 2018, motorcycle riders accounted for 40% of all fatalities resulting from a guardrail collision. Following motorcycle riders were car occupants, with 31% of all fatalities in this crash mode. This is particularly surprising as cars compose approximately half of the vehicle fleet (46%) while motorcycles comprise only 3% of the registered vehicles. In terms of fatalities per registered vehicle, motorcycle riders are overrepresented in the number of fatalities resulting from guardrail impacts. There are currently no guidelines available to U.S. transportation agencies, policymakers, or engineers for how to protect motorcyclists who strike traffic barriers. MASH crash test procedures, which have been successful in ensuring safer barrier designs for cars and light trucks, do not prescribe a crash test procedure for motorcycles. Most research in the area of motorcyclist- friendly barrier or motorcycle-barrier crash testing has been conducted in either Europe or Asia. Little has been published in recent years on the characteristics of this issue in the United States or on potential solutions. The objective of this research program was to identify the factors that contribute to serious and fatal injury in motorcycle collisions with traffic barriers. The focus of this project was on collisions with guardrail, concrete barrier, and cable barrier, and the factors that influence injury given that a crash has occurred. The longer term goal is to establish priorities for U.S. transporta- tion agencies and roadside safety engineers seeking to remediate the injury and fatality risk of motorcyclist-barrier collisions. 11.1.1 Constraints on Injury Mitigating Strategies It is important to emphasize that motorcyclist-barrier fatalities should not be reduced at the expense of passenger car occupants involved in barrier collisions. Guidelines such as MASH and NCHRP Report 350 have described ways of safely redirecting errant vehicles onto the road without undue occupant risk. Cable barriers or any other type of barrier should not be removed just to protect motorcyclists. Rather what is needed are barrier designs, safety programs, and research that can extend the safety record of barrier performance in car collisions to encompass motorcyclists. The goal is to develop methods that can better protect motorcyclists without reducing the benefits of traffic barriers for passenger vehicle occupants. C H A P T E R 1 1 115Â Â
116 Motorcycle Crashes into Traffic Barriers: Factors Related to Serious and Fatal Injuries 11.1.2 Anticipated Research Results The objective of this research program is to determine the factors associated with serious and fatal motorcycle crashes associated with traffic barriers. Following is a list of the research questions pursued in this program: ⢠Determine the risk of fatality and injury by barrier type to include W-beam, cable barrier, concrete, bridge rails, and crash cushions. Are some barrier designs safer than others? ⢠For each barrier type, determine the distribution of injury and injury by barrier component. For W-beam barrier, for example, does the risk of injury from the posts differ from the risk of injury from impact with the rail? ⢠Establish the frequency and severity of injuries in motorcycle-barrier crashes by body region (head, chest, lower extremity). What should the priorities be for rider protection? ⢠Estimate the ratio of fatalities caused by motorcyclists vaulting over a barrier versus sliding into a barrier. Which crash mode should be the priority for a motorcycle-barrier crash test? ⢠Find the ratio of motorcyclists already seriously or fatally injured by contact with the ground or other objects prior to impact with the barrier. Is there any evidence for the hypothesis that the life-threatening injuries occur from ground impact before riders collide with the barrier? ⢠Changes in the post shape have been proposed as an injury countermeasure. Is there any evidence of the I-beam edges cutting the rider? ⢠What roadway geometries are associated with the incidence of motorcycle crashes with traffic barriers? ⢠What are the options for dynamic crash testing of motorcycles into traffic barriers? ⢠What countermeasures are available to protect motorcyclists in collisions with barriers? 11.1.3 Gaps and Research Needs The literature review identified a number of gaps in the literature and research needs for U.S. motorcyclists. Following is a summary: ⢠There are currently no guidelines available to U.S. transportation agencies, policymakers, or engineers for how to protect motorcyclists who strike traffic barriers. ⢠On U.S. roadways, the trade-offs between colliding with traffic barriers versus the fixed objects (e.g., utility poles) that may exist behind these barriers are unknown. ⢠There is only limited information on U.S. roads of rider impact configuration (i.e., sliding or upright) when striking a longitudinal barrier. ⢠There is no recent information on rider injury patterns in U.S. motorcyclist-barrier collisions. These injury causation mechanisms are needed to prioritize longitudinal barrier design or selection of MPS. ⢠It is unknown how barriers certified in MASH crash tests would perform if retrofit with MPS. ⢠The current most widely accepted crash test, CEN TS 1317-8, only tests riders who slide into a barrier, and only considers head and neck injuries. Missing is a test for the approximately half of all riders who strike barriers while upright and/or at risk of thoracic injuries, the most common serious injury mode. 11.1.4 Analysis of Fatal Motorcycle-Guardrail Crashes in the United States Fatal crash trends in the United States were investigated to determine where fatal guardrail crashes were most likely to occur as compared to all fatal motorcycle crashes. For this study, data from FARS from 1999 to 2008 were analyzed. Over this time period, there were 38,254 fatal motorcycle crashes involving 39,468 fatally injured motorcycle riders and passengers. There were 1,759 fatal motorcycle-guardrail crashes over the same time period, fatally injuring 1,803 motor- cycle riders and passengers, an average of 180 fatalities each year.
Conclusions 117Â Â Fatal motorcycle-guardrail crashes were almost exclusively single-vehicle crashes, though over 50% of all fatal motorcycle crashes are multi-vehicle crashes. About three-quarters of fatal guardrail crashes occurred on curves. Riders fatally injured in motorcycle-guardrail crashes tended to be younger than the overall population of fatally injured motorcyclists. 11.1.5 Fatality Risk in Roadside Motorcycle Crashes in the United States Guardrails and other barriers are not the only obstacles that exist on the roadside. Although this study focused primarily on barrier collisions, other roadside objects pose a great risk to motorcyclists. This component of the study investigated the national risk of fatality in collisions with trees, signs and poles, guardrails, and concrete barriers. The FARS data from 2004 to 2008 was used to determine the number of fatalities in each collision mode, and the NASS GES data was used to estimate the total number of crashes in each collision mode. This analysis was based on over 3,600 fatal motorcycle crashes with roadside objects and an estimated total of nearly 20,000 crashes with roadside objects. Risk of motorcycle collision with roadside objects was compared to that of single-vehicle motorcycle collisions where the motorcycle did not strike anything except for the ground. Motorcycle crashes with roadside objects resulted in a greater risk of fatal injury than colli- sions with the ground. Based on the MHE reported in the crash, motorcycle collisions with guardrail were 7.2 times more likely to be fatal than collisions with the ground. Collisions with concrete barrier were 4.1 times more likely to be fatal than collisions with the ground. This is an early indication of the importance of barrier design. The risk of fatality in a guardrail collision is nearly double that of a collision with concrete barrier. A crucial point is to consider the potential consequences of collisions with what the barrier was shielding. Collisions with trees had a fatality risk nearly 15Â times greater than the fatality risk in collisions with the ground. Thus, if a motorcyclist crashes into a barrier in place to protect users from roadside trees, the barrier is likely to have reduced injury severity. Though there is no way to determine what the injury severity would have been had the motorcyclist struck the tree, a collision with a tree may have been a more severe crash than if the rider struck the guardrail. 11.1.6 Risk of Serious Injury in Barrier Crashes One key aspect of this research program was to determine whether some barrier designs are safer than others. Are cable barriers more dangerous than other barrier types? The initial study on fatality risk showed the importance of design: guardrail barrier collisions carried a greater risk of fatality than concrete barrier collisions. This question was further investigated by analyzing barrier crashes of all injury severities in three states: North Carolina, Texas, and New Jersey. The analysis dataset contained 1,000 riders involved in barrier crashes in the three states. Of these, 581 cases were involved in W-beam crashes, 367 cases were involved in concrete barrier crashes, and 52 cases were cable barrier crashes. This study found that W-beam guardrail had significantly higher odds of serious (K+A) injury than concrete barrier. This is consistent with the earlier analysis of fatality risk. The odds of serious injury in crashes with W-beam guardrail were about 1.4Â times greater than those in crashes with concrete barrier. There was no evidence to show that cable barrier posed a greater risk to motorcyclists than either W-beam or concrete barrier. However, we caution that the sample of cable barrier crashes was small compared to the sample of W-beam and concrete barrier crashes. This initial analysis showed no elevated risk of serious injury in cable barrier crashes. However, further investigation is needed to demonstrate if this finding is a result of the dataset used or is representative of most crashes.
118 Motorcycle Crashes into Traffic Barriers: Factors Related to Serious and Fatal Injuries 11.1.7 Relationship Between Rider Post-Impact Trajectory and Injury Outcome in Barrier Crashes The objective of this study was to characterize the rider orientation and post-impact trajectory in a barrier collision, and determine how this orientation influences the injury outcome. The international literature is not consistent on this basic question. Resolution of this question is needed to design a representative crash test (should the rider slide into the barrier or be upright?) and to determine priorities for countermeasure design (is post padding or reducing the sharp upper edge of W-beam more important?). Rider trajectories in barrier collisions were determined through an analysis of PARs of motorcycle-barrier crashes in New Jersey from 2007 to 2011. In a motorcycle-barrier collision, the rider will frequently separate from the motorcycle, and the two may follow different trajec- tories. We defined post-impact trajectory as the trajectory taken by the rider after the motorcycle collides with or contacts the road, barrier, or other object. Seven different trajectory types were identified: upright, sliding, vaulting, ejected (same side landing), ejected (side unknown), ejected into barrier, and separated prior to barrier impact. Of the 442 single-vehicle, motorcycle-barrier collisions reported in New Jersey, the PAR was analyzed for 430 crashes, and the barrier was identified for 342 of these crashes (77.4% of all crashes). The majority of riders in our study (68.0%) in single-vehicle barrier crashes collided with the barrier while upright. Another 20.0% of riders slid into the barrier. Our findings show a higher prevalence of upright collisions and lower estimates for the prevalence of sliding collisions compared to previous literature. Using German data, Berg et al. (2005a) found that 51% crashed upright and 45% crashed while sliding. Using Australian data, Bambach et al. (2012) found that 44% of fatally injured riders in W-beam crashes crashed into the barrier while upright. In our dataset, 52% of all fatally injured riders in W-beam crashes were upright, which is consistent with the findings of Bambach et al. (2012). However, using French data, Quincy et al. (1988) found that in 58% of crashes riders slid into the barrier. Some of the differences may be regional in nature. Our study looks at U.S. crashes, whereas previous studies have analyzed crashes in Europe and Australia. Rider post-impact trajectory, however, was found to be a significant predictor for serious injury. Being ejected from the motorcycle after impacting the barrier was found to increase odds of serious injury compared to crashes striking the barrier upright. Additionally, being ejected into the barrier also increased the odds of serious injury (4.7 times higher than non-ejected). 11.1.8 Analysis of Injuries from Roadside Collisions in Maryland Motorcycle-to-barrier collisions were characterized through retrospective studies of national and state crash databases. These studies can quantify the number of motorcyclists who are seri- ously or fatally injured, but do not directly answer the question of how motorcyclists are being injured. To identify the opportunity for design improvements to the roadside to reduce the severity of these crashes, the injuries incurred must first be better understood. To determine the type, relative frequency, and severity of injuries incurred in motorcycle roadside crashes, CODES was used to analyze motorcycle crashes in Maryland from 2006 to 2008. CODES links police-reported crashes to hospital data, providing detailed information about injuries incurred during collisions. This study focused on four types of motorcycle crash modes: single-vehicle barrier crashes, single-vehicle fixed object crashes, multi-vehicle crashes, and single-vehicle overturn-only crashes. The analysis was based on injury and crash data for 1,707 motorcyclists involved in these four crash modes.
Conclusions 119Â Â The most commonly injured regions for all motorcycle crashes were the upper and lower extremities. Over 70% of motorcyclists involved in the crashes analyzed suffered an injury to the upper and/or lower extremities. Though extremities were the most commonly injured region, they were not the most commonly seriously injured body region. The thorax was the most frequently seriously injured body region in all types of motorcycle crashes, with the exception of multi-vehicle crashes. Additionally, motorcyclists involved in barrier crashes were about two times more likely to suffer a serious injury to the thoracic region than motor- cyclists not involved in barrier collisions. The most common injury for motorcyclists involved in barrier collisions was a lung contusion, whereas the most common injury for motorcyclists not involved in barrier collisions was a hemothorax or pneumothorax. In the study of injuries in Maryland crashes, riders that impacted a barrier had a higher risk of AIS 2+ laceration than riders in other types of collisions based on the point estimate, though this was not found to be significant. One hypothesis was that the lacerations were caused by rider impact with the edges of the guardrail posts and the upper and lower edges of the W-beam. 11.1.9 Roadway Characteristics Associated with Motorcycle Crashes into Longitudinal Barriers and the Influence on Rider Injury This study provides an analysis of roadway and specific geometric characteristics associated with motorcycle-to-barrier crashes in two states based on a total of 1,511 crashes occurring in Washington and Ohio. Motorcycle impacts with barriers were found to be overrepresented on horizontal curves and on sections with grade in excess of 3% in comparison to all single- vehicle motorcycle and all multiple-vehicle motorcycle crashes. Similar to previous studies, these crashes also were found to be overrepresented on ramp sections. Based on the available curvature data, however, the sole recommendation in the available published literature to place potential motorcycle-to-barrier crash countermeasures on curves with a radius less than 820 ft may not be prudent in the United States, as less than 40% of these crashes occur on these curves. Although there were a number of similarities in motorcycle-to-barrier roadway characteristics between the two analyzed states, large differences were found in areas, including roadway configuration (e.g., divided/undivided) and posted speed limit. Rider characteristics, such as helmet usage and alcohol involvement, were found to have a larger influence on injury severity in comparison to associated roadway characteristics. Whether or not the roadway was divided was found to be the roadway characteristic having the largest influence on rider injury. The developed models suggest that horizontal curves, vertical grades less than 3%, posted speed limits greater than 45 mph, and traffic volumes less than 10,000 vpd increase rider injury risk, although these results were not statistically significant. 11.1.10 In-Depth Investigation of Injury Mechanisms To determine injury mechanisms in motorcycle-to-barrier crashes, Virginia Tech collaborated with the Wake Forest Baptist Medical Center (Winston-Salem, NC) to conduct a series of in-depth crash investigations of motorcyclist-barrier collisions. Cases in our study were identified and enrolled by Wake Forest Baptist Medical Center (Winston-Salem, NC) from patients involved in single-vehicle motorcycle crashes with roadside barriers who were admitted to their Level 1 trauma center. The study investigated 21 serious motorcycle-to-barrier crashes, involving 22 riders. In these crashes, the most common regions to suffer the most serious injury were the head, lower
120 Motorcycle Crashes into Traffic Barriers: Factors Related to Serious and Fatal Injuries extremities, and thorax. The thorax suffered the greatest number of serious injuries. The extrem- ities suffered the most injuries; however, these tended to be less severe than injuries in other body regions. These findings are consistent with those presented in our Maryland CODES study and the Bambach et al. (2012) study. In most of the crashes investigated, the guardrail prevented the rider from a potentially more hazardous collision with trees. As found in the earlier study on fatality risk, collisions with trees carry a higher fatality risk than collisions with guardrail. Additionally, in several of the cases, the guardrail likely prevented the rider from traveling over a cliff or embankment. Therefore, though guardrail collisions are severe, removing the barriers is not the solution to the problem. The study has shown that the primary injury mechanisms in our sample were (1) rider entanglement with posts; (2) lacerations from top of posts, both W-beam and cable barrier; and (3) laceration from the top of W-beam rail. Of note are our observations on cable barrier (i.e., wire-rope barrier) collisions. Despite the concern of laceration injuries by motorcyclists con- tacting wire-rope barrier, we found no evidence of laceration injuries from the wire rope in these systems. Injuries were found in collisions with wire-rope barrier, but the injuries resulted from contact with the posts rather than with the wire rope. This clinical finding is consistent with the conclusions from our bulk accident study conducted using state crash data, which found no statistically significant difference between the injury risk of W-beam and cable barrier, both systems supported by unprotected posts. 11.1.11 Existing MPS for Motorcycle-Barrier Crashes Several potential countermeasures currently exist to mitigate the consequences of a motorcycle- barrier impact. These devices, typically referred to as MPS, generally fall into two categories: (1) devices that reduce the severity of post impact through post redesign or shielding, and (2) devices that prevent impact with the post by the addition of a lower rail element or redesign of the rail element. These MPS have been installed in multiple locations in both Europe and Australia. Publications on testing experience with these devices are relatively limited. This was especially true for evaluating the effect that these countermeasures might have on passenger vehicle impacts. The publications that were available on the performance of these devices indicate that they are likely to reduce the severity of motorcycle-barrier crashes. Two pilot tests of MPS have been conducted to date in the United States. The first was con- ducted by Caltrans and the second by NCDOT. Both pilot tests used the Lindsay Transportation Systemâs DR-46 Barrier Attenuator system. 11.1.12 Crash Tests Options for MPS There are currently four crash test procedures for evaluating MPS: the French LIER procedure, the German BASt procedure, the Spanish UNE 135900 procedure, and the European Technical Specification CEN TS 1317-8. The most widely accepted procedure is the European Technical Spec- ification CEN TS 1317-8, which specifies a full-scale crash test to evaluate the performance of MPS affixed to longitudinal barrier. The CEN TS 1317-8 test is designed to emulate the situation in which a rider leaves the motorcycle and slides along the ground into a barrier. In this test, an ATD (commonly referred to as a crash test dummy) is slid at an angle into a barrier at either 60 or 70 km/h. The test prescribes limits on loads to the head and neck of the dummy. Currently, CEN TS 1317-8 does not prescribe a test for motorcyclists who strike barrier in an upright posi- tion, which is estimated to account for over 50% of all collisions.
Conclusions 121  11.2 Recommendations This study is one of the first in the United States to investigate the factors leading to serious injury in motorcycle collisions with roadside barriers. The United States currently does not provide transportation agencies or the roadside safety community any guidelines on how to reduce the risk of injury for motorcyclists in collisions with a traffic barrier. This report has discussed the elevated risk faced by motorcyclists who experience these collisions, the efforts undertaken by regulators in Europe and Australia to address this issue, the design of production MPS, and potential crash tests to evaluate the crash performance of these countermeasures. Based on these findings, this study suggests the following next steps: ⢠Evaluate field performance of U.S. pilot tests of MPS. Two pilot tests of MPS have been conducted to date in the United States. The first was conducted by Caltrans and the second by NCDOT. Both pilot tests used the Lindsay Transportation Systemâs DR-46 Barrier Attenuator system. Evaluation of the field performance of these pilot programs should be conducted in terms of motorcycle and four-wheeled vehicle safety, installation experience, and the practicality and costs of maintaining these systems. ⢠Evaluate EN 1317-8 test in the United States. The most widely accepted motorcycle-barrier crash test procedure is the European Technical Specification CEN TS 1317-8. This test simulates the crash performance of MPS affixed to a longitudinal barrier. This test should be conducted on U.S. roadside hardware that has been evaluated using MASH test procedures, both to check the performance of U.S. hardware in this crash mode, and to evaluate the test procedure itself. ⢠Evaluate crash performance of MPS for four-wheeled vehicles. One obstacle to widespread retrofit of MPS to existing barrier systems is that the crash performance of these retrofit systems for four-wheeled vehicles has not been determined. It is important that the successful crash performance of traffic barriers should not be reduced by the installation of retrofits to protect motorcyclists. The recommendation is to evaluate the performance of MPS-equipped barriers in standard MASH crash tests using four-wheeled vehicles (e.g., small cars and pickup trucks). ⢠Develop a MASH motorcyclist crash test. MASH currently does not prescribe a crash test for motorcyclists striking roadside hardware. Adoption of the European EN 1317-8 test is one option. There may be regional differences, however, which may require that other crash test options be considered as well. For example, this NCHRP project has estimated that riders striking a barrier upright occurs much more frequently than suggested by studies in Europe. An MPS test that uses an upright rider should be developed. Development of a new test should consider an enhanced MPS test that evaluates the risk to the thorax and lower extremities, which our study has shown to be the most frequently seriously injured body regions. ⢠Considerations for the AASHTO Roadside Design Guide. Potential additions to the AASHTO Roadside Design Guide should be considered for how to locate longitudinal barrier that incorporates the differences between the road departures of four-wheeled vehicles and motorcyclists. Factors in the development of these guidelines would be differences in trajec- tories, departure angle, departure speed, and the magnitude of evasive maneuvers (e.g., braking). NCHRP Project 17-88, which is characterizing motorcycle roadside departures in comparison to four-wheeled vehicle departures, may provide useful guidelines for this evaluation. ⢠Develop methods to determine where to locate MPS. The installation of MPS carries a cost, and should be considered where it would be more beneficial. Potential methods for determining suitable MPS locations include traditional hot-spot methods or the empirical Bayes methods used in the FHWA Highway Safety Manual. Cost-benefit methodologies for MPS location should be developed.
122 Motorcycle Crashes into Traffic Barriers: Factors Related to Serious and Fatal Injuries This study has important implications for U.S. federal and state transportation agencies seeking ways to reduce the risk of serious-to-fatal injury for motorcyclists. The findings show the need for the adoption of MPS that either pad or shield the posts to prevent motorcyclist entanglement and protect riders from laceration from the tops of rails and posts. MPS have been implemented in Europe and Australia that have tremendous potential to mitigate injuries in barrier collisions. This research program has shown the need for MPS in the United States, the feasibility of these systems, and their potential safety benefit for U.S. motorcyclists. After a thorough evaluation of MPS in crash testing and pilot testing in the United States, our recom- mendation is that MPS should be considered for implementation on U.S. roadways.
