Understanding the Problem
Due to the complexities of the transportation system and how humans interact within it, risks to road users outside the vehicle can exist in unexpected ways (Naumann et al., 2019, 2020). Collaborative planning, engineering, vehicle regulation, road user safety enforcement and education and technology-based strategies are all needed to reduce latent risks. Bicyclist behavior is not only a product of the characteristics of the individual bicyclist but is also sensitive to greater influences of the socio-ecological environment, from the characteristics of the roadway to the nature of the trip or destination, to the degree of social acceptance for bicycling in the community. Finding solutions requires thinking beyond specific site properties or individual road user actions. Creating a safer environment in which people on bicycles and drivers of motor vehicles can safely interact while at the same time ensuring that persistent structural inequities are not perpetuated demands a systemic focus.
Bicyclists are especially vulnerable to crash energies in a collision with a motor vehicle. The most effective means of protecting them is to eliminate conflict with motor vehicles. The Hierarchy of Controls diagram, adapted from workplace safety practices, illustrates safety mitigation strategies from most effective to least effective. Proactively eliminating high level risks at the population level, while addressing systemic inequities, such as the process by which bicycle facility investments are prioritized in some areas of communities and not others, is more effective for more people than a focus on individual protective measures.
Hierarchy of Controls for Traffic Safety
Separated bicycling infrastructure, which removes the risk of a collision with a motor vehicle for people on bicycles, is an example of an elimination strategy. A key substitution strategy is one of mode shift – replacing car trips with bicycling or walking trips reduces exposure of all road users to motor vehicle traffic and reduces kinetic energy (crash forces) in the system, thereby mitigating injury severity if a crash occurs. Engineering controls are efforts to impact driver and other road user behavior through vehicle design and roadway infrastructure. Examples include methods that mitigate driver speed or increase visibility of vulnerable road users, such as trimming roadside vegetation. Crash and injury mitigation methods such as targeted efforts to manage speed, reduce distraction and impairment, and addressing aggressive or risky driving behaviors can be critical for improving bicyclist safety. These efforts can be tackled through administrative controls, by way of policy, legislation, enforcement, or other behavior change programming. Personal protective equipment such as active lighting and bicycle helmets are important individual measures for protecting people on bicycles.
Gaining a better understanding of the diverse experiences of people walking and bicycling and how risks and outcomes may vary across populations is crucial to identifying, prioritizing, and implementing safety interventions. Inequitable investment in safe bicycle facilities has resulted in less safe built environment conditions for some populations. In a review of more than 7,000 bicyclist crashes in California’s San Francisco Bay Area, among five racial/ethnic groups, Black bicyclists were involved in the most crashes per person per distance traveled (Barajas, 2018). The crash rate per person per distance traveled for Black bicyclists was nearly eight times that of white bicyclists; the rate for Hispanic bicyclists was 2.5 times greater than that of white bicyclists. In Washington State, an analysis of bicycle collisions along main street highways (State routes that also function as main streets for local residents) found that low-income areas and communities with large minority populations have a higher probability of collisions involving a motor vehicle (Moudon & Kang, 2017). A study conducted for the Florida Department of Transportation concluded the built environment in low-income communities put people on bicycles at greater risk of being struck by motorists (Dumbaugh et al., 2020).
Tailoring of program delivery may be needed to address diverse populations, such as recent immigrants who may not be familiar with U.S. traffic laws, the U.S. traffic environment, or who may not speak or read English. Behavior on a bicycle can be a factor of age and ability. People who ride bicycles come in all ages with many levels of knowledge, skill, perception, and judgment. Children, who are at different stages of cognitive development, have less experience with the roadway environment, are less aware of their limitations, and are especially prone to errors that may place them in dangerous situations (Almeida et al., 2016; Hamann & Peek-Asa, 2013; Plumert & Schwebel, 1997; Schwebel & McClure, 2014). Older adults riding bicycles may experience reductions in vision, hearing, agility, balance, speed, and strength (Tournier er al., 2016). People living with disabilities who may also be riding bicycles or adaptive bicycles may face challenges navigating certain roadway locations, though research on the safety needs for those bicycling with disabilities is lacking (MacArthur et al., 2020). Agencies should select countermeasures to address problems identified within communities or common to a high-risk group within a community, such as older adults, people experiencing homelessness, or children. Moreover, educational and enforcement programs must take these factors into account and be designed to target specific concerns and the knowledge, skills, and behavioral attributes of these different groups of riders.
The countermeasures described in this report relate primarily to legislative, policy, program, and enforcement measures aimed at improving the knowledge and behaviors of road users to prevent or mitigate the severity of crashes but are not intended to be used in isolation or absent a continued focus on the entire transportation system and the environment surrounding people on bicycles.
Countermeasure selection for improving bicyclist safety will require collaboration across agencies and disciplines. Reducing or eliminating exposure to known risky situations through comprehensive behavioral and environmental countermeasures (without necessarily discouraging bicycling) via strategies such as reducing motor vehicle volumes and creating physical space for all road users, will have the greatest impact on bicyclist safety over the long term.
Roadway and urban design
The importance of road design and the built environment in fostering safer user behaviors is supported by a body of research, and it is essential to consider context when planning countermeasures. Infrastructure countermeasures can be informed by knowledge and expertise present in SHSOs. Agencies can participate in road safety audits and provide valuable insights to help identify where communities should target engineering resources to improve safety.
Most fatal bicyclist crashes occur in urban areas, where more people are riding bicycles (NCSA, 2022). In urban areas, there are many locations with high potential for conflicts, and motor vehicle traffic is moving on roads primarily designed for cars. The presence of intersections, driveways, shops, or apartment blocks, for example, can create conflicts and higher, more concentrated traffic volumes (Monsere et al., 2017). A review found relationships between overall crash numbers and motorist maneuvers such as turning, overtaking, opening a door, or pulling out from parking spaces, so roadway environments where more of this is taking place could be riskier for bicyclists (Prati et al., 2018). A comprehensive approach, involving partnerships with State or local roadway engineers, that uses a combination of effective engineering, enforcement, and educational measures may have the best chance of achieving desired crash reductions.
A focus on driver behavior, such as reducing motor vehicle speeds, is an important step in improving safety for all road users, especially people on bicycles. Likewise, decreasing risky behaviors such as aggressive driving, distraction, and impairment will also positively effect bicyclist safety. Bicyclists, as unprotected or vulnerable road users, are more susceptible to crash forces than motorists who are protected by the safety features installed in motor vehicles. In some extreme cases, motorists exhibit aggressive behavior towards bicyclists, based on their beliefs or perceptions about the bicyclist. While this behavior is not common, it does represent a threat to people on bicycles using the road and may play a role in overall safety outcomes (Piatkowski et al., 2017).
A majority of bicycling fatalities occur at non-intersection locations and speed is frequently a factor in these fatalities due to the kinetic energy involved when a faster, heavier vehicle strikes a slower moving bicyclist (Cushing et al., 2016). Research has shown the likelihood of a bicycle crash being fatal increases substantially when vehicle speeds exceed 20 mph (Cushing et al., 2016). A study conducted in Sweden indicated that in urban areas a reduction in posted speeds from 50 to 60 km/h to 30 to 40 km/h (~31 to 37 mph to 19 to 26 mph) lowered the risk of a serious injury in bicycle/motor vehicle collisions (Isaksson-Hellman & Töreki, 2019). See more in the chapter on Speeding and Speed Management.
Motorist overtaking crashes are the most common fatal crash type for bicyclists in both urban and rural areas (Thomas et al., 2019). Studies have used instrumented motor vehicles, instrumented bicycles, or other video data to measure motorist passing distances and have found relationships between passing distances and variables related to roadway configuration, traffic conditions, and motorist and bicyclist characteristics. A recent evaluation of HVE campaigns showed improved overall passing distances and a reduction in passing distance violations (Blomberg et al., 2022).
People who drive motor vehicles while impaired pose a great danger to people on bicycles. In 2020 of the 930 crashes resulting in a bicyclist fatality, 125 of those crashes involved an alcohol-impaired motor vehicle driver (NCSA, 2022). In 2020 34% of all crashes resulting in a bicyclist fatality involved alcohol consumption by either the motorist or the bicyclist (NCSA, 2022).
The risk of a crash may be increased due to inattention or distraction, by either the cyclist or driver. While impaired driving and riding have been an ongoing challenge, emerging problems include the use of cell phones, media players, or other electronic devices while riding or driving. Feng et al. (2018) used naturalistic driving data from instrumented motor vehicles to examine events where motorists passed bicyclists and found that approximately 7.8% motorists in passing events were actively engaged with using their cell phones and that those motorists conceded less space to bicyclists than non-distracted motorists. For a bicyclist, this means that 1 in 13 passing events may involve a cell phone distracted driver.
Literature searches do not identify any studies that have evaluated laws or programs aiming to reduce distracted riding. A survey of bicyclist attitudes and behaviors indicates that 21% of bicyclists use an electronic device on at least some of their bicycle trips, with 9% indicating they use a device during nearly all their trips (Schroeder & Wilbur, 2013). An observational study of 1,974 bicyclists in Boston, Massachusetts, found that 31.2% of riders were distracted, however the distractions were defined very broadly as wearing earbuds or headphones (17.7%) and having an object or mobile phone in their hand or on the handlebars (13.5%) (Wolfe et al., 2016). Currently, there is a lack of information about the impact of distracted bicycling on bicyclist safety (Mwakalonge et al., 2014).
Some studies have focused on the role of motor vehicle type and design in the event of a crash. Ackery et al. (2012) found that larger motor vehicles—especially freight trucks and SUVs—were overrepresented in bicycle crashes compared to other vehicle types. In an examination of national and State level crash data, Hu and Cicchino (2022) found that minivans, large vans, pickups, and SUVs collectively had higher likelihood of being involved in certain types of crashes involving pedestrians. Increased involvement of heavier vehicles can lead to greater injury severity and is an important consideration when implementing speed management and driver behavior strategies.
Mandatory Helmet Laws
Helmets are important protective gear that can reduce injury severity from single-vehicle crashes and from collisions with motor vehicles. There is a large body of research on the protective effects of helmet use, but there is currently not consensus on whether mandatory helmet use laws are the most effective means of increasing the use of helmets and ensuring population-wide access to the protection that bicycle helmets offer. Research has shown that community-based interventions such as helmet promotion accompanied by free helmets has proven effective at increasing helmet use while addressing inequitable access to helmets (Owen et al., 2011).
Several meta-analyses conducted over the past 2 decades have concluded that bicycle helmets are effective at reducing head injuries among bicyclists involved in falls or crashes with a motor vehicle (Attewell et al., 2001; Elvik, 2013; Høye, 2018b; Olivier & Creighton, 2017; Thompson et al., 1999). The most recent meta-analysis found that the use of bicycle helmets reduced head injuries by 48%, serious head injury by 60%, traumatic brain injury by 53%, face injury by 23%, and the total number of killed or seriously injured bicyclists by 34% (Høye, 2018b). A study that examined emergency room visits of children that had bicycle-related injuries found that unhelmeted children were more likely to sustain injuries (40% versus 25.7%), meet the trauma activation criteria (45.5% versus 16.8%), and be admitted to the hospital (42.4% versus 14.9%). Overall, injury severity was worse with unhelmeted children, and these children were significantly more likely to have brain injuries, skull fractures, and facial fractures (Michael et al., 2017).
It is likely that bicycle helmets have a larger effect in single bicycle crashes than in bicycle crashes with motor vehicles (Høye, 2018a). A small study examining medical data from a set of cycling fatalities found helmets could have a positive (lifesaving) effect in bicycle-only crashes, but often would not have prevented the fatality in high-energy crashes with motor vehicles or trains, often due to the difference in momentum (Bíl et al., 2018). Swedish researchers applied a systems approach to investigating bicycling fatalities, and an analysis of police-reported crashes, medical records, autopsy reports, accident analyses and witness statements, estimated that helmets could have saved 46% of the non-helmeted riders (Kullgren et al., 2019). Examination of bicyclist injuries across seven Seattle area hospitals did not find an association between risk of serious injury and helmet use. However, they did find a strong relationship between motor vehicle involvement in the crash and injury severity. Though fatalities were rare events in the data used for this study, the authors did find an association between helmet use and fatal injury, with nonhelmeted riders being more likely to die than helmeted riders (Rivara et al., 2015). Motor vehicle involvement similarly increased likelihood of a fatality. Helak et al. (2017) looked at outcomes as reported in the National Automotive Sampling System – General Estimates System (NASS – GES) and found no significant differences in police reported injury severity if the rider was wearing a helmet versus not wearing a helmet.
While helmet use is important for preventing serious head injuries among all ages, some jurisdictions are concerned mandatory helmet use legislation for all ages will discourage bicycling, perpetuate existing inequalities in access to helmets, or lead to inequitable enforcement of the law. Disparities in access and means to obtain helmets have been observed. A study measuring racial disparities following a helmet law found that helmet use among Black high school students increased less than among their white counterparts, and that these disparities persisted over time (Kraemer, 2016). Exploration of trauma registry data showed that among children under age 16 who were admitted to a trauma center, non-helmeted children were more likely to be Black or insured by Medicaid (Gulack et al., 2015). Selective enforcement of bicycle-related minor violations such as mandatory bicycle helmet laws, especially against low-income people and people of color is a concern. Officers may use issuing bicycle-related citations as an excuse to stop, question, or search people, which may lead to reduced ridership among groups who feel especially likely to be targeted (Brown, 2021; National Association of City Transportation Officials [NACTO], 2016). Given that increased riding provides health benefits, some agencies prefer to use encouragement in lieu of a law to increase helmet use by adults.