Bicycle-related injury and fatality rates can be reduced by preventing crashes and reducing the risk of injury, or at least its severity, should a crash occur. ("Crash" is a better term than "accident"—see below.) Bicyclists can use helmets, if fitted properly, to substantially reduce the risk of a head injury in the event of a crash. This is crucial because head injuries are responsible for most permanent and fatal injuries which happen to cyclists. Cycling gloves can prevent major injuries when the hands are used to break a fall. Although more widespread helmet use can reduce the incidence of fatalities and serious and permanent injuries, some fatalities, many serious injuries, and the majority of non-serious bicycle injuries can only be prevented by reducing the crash rate.

Because bicycling is a low-impact activity, if crashes can be avoided it is one of the safest forms of aerobic exercise and an easy way for those out of shape to gradually become more fit. Americans do not get enough exercise: "Despite common knowledge that exercise is healthful, more than 60 percent of American adults are not regularly active, and 25 percent of the adult population are not active at all" (CDC 1996).

Incorporating exercise into one’s daily routine is necessary to get the regular exercise that health promotion experts advise ("30 minutes of physical activity of moderate intensity [such as brisk walking] on most, if not all, days of the week) (CDC 1996). Cycling for transportation is one way people can get a daily workout without making time for exercise.

Studying bicycle crashes helps in identifying countermeasures—methods to prevent future crashes. Data on previous crashes come from several sources:

Bicyclist surveys. This is the only method providing both complete event data (minor and major injuries) and some data on "exposure" (number of miles ridden), but provides no information on fatalities.

Hospital records. These in theory could provide complete data on injuries that were serious enough to require a visit to an Emergency Room.

Police records. In most jurisdictions, only crashes involving at least one motor vehicle are recorded, so the majority of bicycle crashes (those that do not involve motor vehicles) are not even eligible to be reported. In Moritz’s 1998 study, 28% of bicycle crashes with $50 or more of property damage or medical expenses were reported to the police.

All of these sources provide some valuable information and are necessary to provide a complete picture.

Falls and crashes with fixed objects happen because of problematic surface conditions and/or bicycle operator error. Many falls produce very minor injuries, but others can result in major injuries or even fatalities. Most bicycling injuries are the result of falling (hitting the ground), whether preceded by a collision or not.

Table 1 Percentage Distribution of Crash Types from Two Studies

The data show that only a minority of bicycle crashes are due to automobiles. As shown in Table 1, car-bike collisions represented 11% of the total reported by club members, and 15% of those reported by emergency rooms. Although car-bike collisions are a small proportion of all bicycle crashes, they are the largest cause of fatal bicycle crashes.

For bicycle club members, bike-bike collisions are almost as common as bike-car collisions. Such collisions can be serious, even fatal, as can collisions with pedestrians and dogs. (Pedestrians can also be injured or even killed by colliding with bicyclists.)

Skidding falls happen when the rear wheel slides out. They typically occur when turning, and when something slippery has reduced the friction between road and tire. Countermeasures include eliminating slippery areas (e.g. some types of paint and thermoplastic, metal grate bridges, and metal covers), improving maintenance to remove sand, gravel, wet leaves, oil, and ice from the roadway, and training cyclists to avoid such areas or, at the least, coast over them without turning.

Diverting falls happen when the cyclist is prevented from turning the front wheel into the lean to maintain his or her center of gravity. These falls can occur when the cyclist rides next to a parallel ridge such as a streetcar track or any seam or ridge in the road. Metal grate bridges and railroad tracks crossing the road at an angle can also produce this type of fall. Countermeasures include removing these road features where possible, and training cyclists about these hazards and the need to either avoid them or deliberately steer over them.

Insufficient speed falls are generally the least serious type. They happen when a cyclist does not, or cannot, remove a foot from a toe clip or "clipless" pedal system soon enough, or when he or she intends to go forward but is suddenly blocked by traffic. The only countermeasure is to improve cyclists’ use of clips and pedal systems.

The most detailed analysis of car-bike collisions can be found in Forester’s Bicycle Transportation, pp. 46-54 (1994). His analysis is based on data from 919 car-bike collisions in four metropolitan areas collected in a study sponsored by the National Highway Traffic Safety Administration (Cross and Fisher 1977). The Hunter et al. (1996) study provides more recent data of the same type, but the published reports do not permit a detailed analysis of the circumstances of collisions. The frequency distributions of crashes by crash type in the two studies are very similar.

Although they are the most feared of all bike crashes, fewer than 10% of car-bike collisions occur when the motorist is overtaking. When they happen, it is usually in rural areas or at night, or when the motorist is impaired or drunk (Forester’s [1994] analysis of Cross and Fisher 1977).

In his analysis of the Cross and Fisher data, Forester found that the cyclist was riding in the roadway in the direction of traffic in only 37% of all car-bike collisions—in the remaining cases, the majority, the cyclist was entering the roadway, riding against traffic, turning or swerving from the curb lane, or riding on the sidewalk. In general, bicyclists are more likely to be at fault (in the sense of disobeying the rules for drivers of vehicles) than motorists when the two collide. The figures in the 1996 Hunter et al. study reveal that the bicyclist was solely at fault in 54% of cases, the motorist solely in 30%, and both were at fault in 30% of car-bike collisions where culpability was determined.

Forester’s analysis shows that car-bike collisions can be grouped by age of cyclist: child (under 13), teen, and adult. Most victims of bike crashes in which the cyclist rides out into traffic are children. Children also account for most of the crashes in which the cyclist swerves or runs a stop sign. Teen cyclists seem to have learned to avoid ride-out and swerving crashes, but they have more intersection crashes, with causes including wrong-way cycling, sidewalk cycling, and turning left from the curb lane. Adults have mostly learned to avoid the mistakes that teens and children make, but they are subject to a variety of crashes involving motorist error, some of which can be avoided by riding skills such as proper lane positioning and emergency maneuvers.

A study of car-bike collisions in the Boston metropolitan area (Plotkin and Komornick 1984) revealed a high incidence of bike hitting car door crashes; these represented 5.3% of all crashes compared to 0.8% in the Cross and Fisher (1977) study. By comparison, motorist overtaking crashes represented only 3.5% of the total. The high rate of car-door collisions and the low rate of overtaking collisions is because the crashes studied were all in urban areas (towns inside Rt. 128), and may be related to the narrow travel and parking lanes common on many urban roads in the area.

Wrong-Way Cycling Cycling against traffic is one of the most dangerous cycling behaviors. The obvious danger of a head-on collision with a lawful cyclist or motorist is only one of several types of crashes caused by wrong-way cycling. A motorist pulling out from a stop sign, commercial driveway, or turning right at a stop sign or traffic signal (including right turn on red) looks in the direction of traffic, not in the direction of the wrong-way cyclist, and then often has no time to avoid a collision. Cyclists riding against traffic accounted for nearly 1/3 of car-bike collisions in the Hunter et al. 1996 study and ¼ in the Boston area study (Plotkin and Komornick 1984).

Red-Light Running In the Boston study, 6.5% of car-bike collisions, a relatively high share, were caused by the cyclist entering the intersection on a red signal (by comparison, in only 2% of crashes did the motorist run a stop sign or red light). Many cyclists in the Boston area (and elsewhere) routinely ignore traffic signals and stop signs. One contributing factor is the lack of enforcement—in most places in the Commonwealth, police departments never give citations to cyclists. Another contributing factor is the traffic lights themselves: many are controlled for at least some portion of the day by an actuator that consists of a loop of wire buried under the asphalt. An unknown percentage of these detectors are set so that they are insensitive to the amount of mass on a bicycle. When a cyclist is the first to arrive on a red light at such an intersection, he or she will not receive a green light until a motorist arrives to trigger the signal. This lack of responsiveness encourages cyclists to go through on red; and indeed, in some cases (such as a side street crossing a main road late at night), the alternative to entering on red may be waiting for a very long time.

Motorist Left and Right Turn The motorist left turn collision occurs when a motorist turns left into an intersection or driveway and hits a cyclist coming from the opposite direction. This is the most common motorist-caused car-bike collision, accounting for 7.6% of urban car-bike collisions in the Cross and Fisher (1977) study and 10.2% in the Boston study (Plotkin and Komornick 1984).

The motorist right turn collision occurs when a right-turning motorist collides with a cyclist to his or her right. It can occur when the motorist has overtaken too close to the intersection, when a cyclist passes on the right, or when the two are parallel, with the cyclist in the motorist’s blind spot. This type accounted for 4.8% of collisions in the Cross and Fisher study and 6% in the Boston area study.

Both of the motorist turn collisions are more likely to occur to adults, which perhaps explains their higher representation in the Boston area, where apparently there is a higher share of adult cyclists compared to the national average. Although these two accident types together account for only 12% to 16% of car-bike collisions, they are a much higher percentage of the collisions which occur to cyclists riding on the roadway with the flow of traffic.

A cyclist can reduce the risk of a motorist left turn collision by being more visible by (1) using a head light at night and (2) riding close to the stream of traffic, not near the curb (nor on the sidewalk). A cyclist can potentially avoid an incipient left-turn collision by turning right, inside the motorist’s turn. Making such a sharp turn is usually possible only if the cyclist has previously practiced making forced turns—taking advantage of the counter-steering principle to get the bicycle leaned over quickly by steering very briefly to the left, and then immediately bring the wheel back to the right and leaning into the turn.

A cyclist can reduce the risk of a motorist right turn collision by moving to the center of the right lane, certainly to the left of any right-turn only lane, when approaching an intersection; by never passing on the right side of a moving motor vehicle, especially not at an intersection or driveway; and by waiting in front or behind, not beside, a stopped motor vehicle when waiting to proceed at an intersection. A cyclist can also potentially avoid an incipient right-turn collision by turning right, inside the motorist’s turn, in the same manner as described above.

Nighttime Safety Certain types of car-bike collisions occur disproportionately at night, including motorist entering from side street or on-street parking, motorist turning left, motorist overtaking, and wrong-way cyclist hit head-on (Forester 1994 based on Cross and Fisher 1977). In the first two of these crash types, the motorist must yield to the bicyclist already in the road, but the motorists headlamps will not be shining on the bicyclist. Therefore the bicyclist needs, and is required by law to use, a headlight to be seen by vehicles in these situations. A significant number of motorist overtaking collisions occur when the cyclist was unseen at night. Increasing the cyclist’s conspicuity from the rear by equipping the bicycle with a red tail light and a brighter, automotive reflector instead of a bicycle reflector, is the key countermeasure for this crash type. None of the crash studies have information on the lack of required nighttime equipment among bicyclists hit. However, because very few of those cycling at night use lights, the contribution of this behavior to the bicycle crash problem is likely to be high. In a Boston study, 15% of cyclists were observed using either a headlight or taillight at night (Osberg, Stiles, and Asare 1998). The headlight is required in Massachusetts (and every other state), although a rear reflector alone meets the legal requirements. Although not required, tail lights are highly desirable and are probably more in use then headlights currently, since low-power, battery-powered red LEDs are available, and since cyclists are often more afraid of being hit from behind than from the front.

The Effect of Experience on Crash Rates

The more years and miles of cycling experience, the lower the crash rate. College students have a lower crash rate than elementary school students, but not by that much considering that college students are adults and typically licensed drivers (see Table 2). Bicycle club members, on the other hand, have a crash rate which is dramatically lower than both other groups (and their crash rates were essentially the same in 1975 and 1996 surveys). Crash rates decline with years of experience, but more rapidly if bicyclists participate in club rides where they may learn from the example of other riders. More commonly, since club riders are a small minority of bicyclists, new riders learn by trial and error to avoid dangerous behaviors, as the above analysis of accident types shows. The learning process takes some time because most cyclists receive no training, neither in formal classes nor from riding with knowledgeable cyclists. On the road, bad habits are rarely punished and safe and lawful riding is sometimes discouraged. Since bicyclists are rarely stopped even for flagrant violations of the traffic rules such as wrong-way riding, they may persist in their bad habits. Further, the frequent advice given to cyclists—stay off the road, or at least stay as far to the right as you possibly can—may hinder the learning of skills such as riding to the left of a right-turn only lane when proceeding straight or preparing well in advance to turn left by merging to the center of the road. Cyclists who perform these maneuvers correctly are sometimes told by motorists, or even police, to get off of the road.

Table 2 Mean Annual Miles of Bicycling and Mean Crash Rates from Five Studies

Risk of Sidewalk and Wrong-way Riding

Bicyclists who habitually ride on the sidewalk and across crosswalks are more at risk than those who ride on adjacent roadways. A 1994 study in California compared the accident rate per mile of sidewalk riding compared to the accident rate for road riding (on the same roads) and found that the rate for sidewalk accidents was 1.8 times greater (Wachtel and Lewiston 1994).

The same California study found that the relative risk of riding the wrong way (against traffic) was 3.6 times as high for those riding with traffic. In Hunter et al. 1996, about 1/3 of all bicyclists hit by cars were riding against traffic. The Boston study found that about ¼ of all cyclists hit were riding against traffic.

Riding on the sidewalk opposite the flow of traffic is more than 4 times as dangerous as riding on the road with the flow of traffic. The California study found that this risk was 4.3 times greater than riding on the road with the direction of traffic.

Contrary to intuition, cyclists riding on bicycle paths (now called "shared use paths") have a higher crash rate than cyclists riding on roads, although not as high a crash rate as cyclists riding on sidewalks (Aultman-Hall and Kaltenecker 1998). The risk of injuries on paths compared to roads has been calculated as 40%, 80%, and 260% higher (Moritz 1998, Aultman-Hall and Kaltenecker 1998, Kaplan 1976). Some of the increased risk may be explained by the greater likelihood of inexperienced cyclists to use paths or sidewalks (Aultman-Hall and Adams 1998). However, the studies of bicycle club members, who are much more experienced than average cyclists, reveal a higher crash rate on paths even for these riders.

Table 3 Region of injury or injuries of Seattle-area bicyclists visiting emergency rooms

Helmet Effectiveness Rivera et al found that 57% of injured cyclists without head trauma were wearing helmets, but only 24% of cyclists with severe brain injuries were wearing helmets. They calculated the implied reduction in risk of head and brain injury as approximately 70% (see Table 4). This figure may understate the effectiveness of helmets because it can be assumed that some bicyclists experiencing a crash did not have injuries requiring medical attention and therefore were not represented in the control group, bicyclists with non-head injuries. Table 4 also shows that helmets are effective in reducing upper facial area injuries, but not at all in lower facial injuries. The study also found that the risk reduction was about the same—70%—for all age groups.

Helmet Fit Helmets must be snug and low against the forehead for maximum effectiveness. The Harborview study (Rivara et al. 1996) asked injured cyclists or their parents to report on helmet snugness, position on the head, use of pads, adjusting of straps, if the helmet covered the forehead, and whether the helmet could be removed while the strap was still fastened. Cyclists who reported their helmets fit poorly were almost twice as likely to suffer head injury as cyclists whose helmets fit best (Rivara et al. 1996). They found that cyclists whose helmets came off during a crash were three times more likely to have head injuries than cyclists with snug helmets. The study also found that parents’ assessment of fit did not correspond well to that of trained personnel using standard protocols.

Table 4 Relative risk reduction of Seattle-area bicyclists visiting emergency rooms

Summary on Helmets The evidence indicates that helmets are effective in reducing head and face injuries. Since head injuries account for most of the serious and fatal injuries that happen to cyclists, wearing a helmet is very important. Other injuries, while more common, tend to be less serious and usually result in a complete recovery. Helmets are much more effective if they fit properly. Helmets should be used when cycling in any location, even where there is no motor traffic, since any fall can result in head injury, and falls are by far the most common cause of injury.

References

Aultman-Hall, Lisa and Michael F. Adams, Jr. 1998. Sidewalk Bicycling Safety Issues. Paper presented at the Transportation Research Board. 77th Annual Meeting.

Aultman-Hall, Lisa and M. Georgina Kaltenecker. 1998. Toronto Bicycle Commuter Safety Rates. Paper presented at the Transportation Research Board. 77th Annual Meeting.

The Centers for Disease Control and Prevention (CDC). 1996. Physical Activity and Health: A Report of the Surgeon General. 

Cross, Kenneth D. and Gary Fisher. 1977. A Study of Bicycle/Motor Vehicle Accidents: Identification of Problem Types and Countermeasure Approaches. National Highway Traffic Safety Administration.

Forester, John. 1994. Bicycle Transportation. Cambridge, MA: MIT Press.

Hunter, William W. Jane C. Stutts, Wayne E. Pein, and Chante L. Cox. 1996. Pedestrian and Bicycle Crash Types of the Early 1990s. U.S. Department of Transportation. FHWA-RD-95-163.

Kaplan, Jerald A. 1976. Characteristics of the Regular Adult Bicycle User. FHWA. National Technical Information Service. Washington, DC.

Moritz, William E. 1998. Adult Bicyclists in the United States—Characteristics and Riding Experience. Transportation Research Board. 77th Annual Meeting.

Osberg, J. Scott, Sarah C. Stiles and Ohene Kwaku Asare (1998) Bicycle Safety Behavior in Paris and Boston. Accident Analysis and Prevention 30, 5, 679-687.

Plotkin, Wendy and Anthony Komornick, Jr. 1984. Bicycle-Motor Vehicle Accidents in the Boston Metropolitan Region. A Study of Reported Accidents Occurring within Route 128 in 1979 and 1980. Boston, MA: Metropolitan Area Planning Council.

Rivara, Frederick P., Diane C. Thompson, and Robert S. Thompson. 1996. Circumstances and Severity of Bicycle Injuries. Snell Memorial Foundation. Harborview Injury Prevention and Research Center.

Wachtel, Alan and Diana Lewiston. 1994. Risk Factors for Bicycle-Motor Vehicle Collisions at Intersections. ITE Journal. September. pp. 30-35.