CHAPTER V

ANALYSIS OF DATA BY SPECIFIC VARIABLES

This chapter analyzes both mileage data and accident data from a standpoint of what effect independent variables, such as age, sex, experience, and similar items, have on the number of miles ridden or the possibility of accident involvement.

ANALYSIS OF MILES RIDDEN

Age and Sex

As Figure 8 shows, on the average the male respondents traveled almost 900 miles more by bicycle over a year's period than the female respondents. This difference of almost 40 percent more mileage by males may reflect the tendency for males to ride on longer trips than females and also that the work or utility trip may not be as easily made by the female due to dress or other restrictions, including harassment by motorists. This latter action was reported by several female respondents. It should be remembered also that the questionnaire was directed at the most active rider in the family. In many cases, a women who did travel a great many miles by bicycle could not respond because a male in the household might have traveled even further.

Topography and City Size

Figures 10 and 11 show how the average annual miles traveled by the respondents differed according to the topography and the size of the metropolitan area where they live. From Figure 10, it appears that L.A.W. members traveled further in areas that could be classified as steep hills or mountainous than those who rode mostly where it was flat or rolling. However, this difference is based on only 6 percent of the respondents riding in steep terrain. Statistical testing showed that there was no significant difference between those riding in flat land and those in rolling terrain.

Years' Experience

Figure 12 shows the average miles ridden in a year stratified by the number of years that the respondent had been continuously riding a bicycle. As a respondent continues to ride a bicycle over a period of years, it appears that he travels further each year. The very low average of 807 annual miles traveled for those respondents with less than one year's experience is probably not representative because these respondents could not provide a full year's mileage figures if they had been riding for less than a year. This was an oversight in the design of the questionnaire and that mileage figure is shown for illustration only.

Auto Availability

If it is to be believed that many cyclists are using bicycles to complete trips that would otherwise have been by other modes, then the miles traveled by bicycle should increase if the respondents have less cars available. As can be seen in Figure 13, this is exactly what happened.

ANALYSIS OF ACCIDENT EXPERIENCE

Age and Sex

While bicycles are becoming more and more of a common sight on streets and highways today, so are reports of injuries and deaths to the cyclist (12). Therefore, it is important to note what influence different variables appear to have on the rate of such incidents. Figures 14 and 15 show the accident involvement rate per one million miles traveled by bicycle for both male and female and for differing age groups.

These diverse findings are difficult to explain, although it might be reasonable to assume that younger riders might experience a higher overall accident rate due to having less experience and possibly the tendency of the young to take more chances.

Cycling Experience

Figure 16 shows the accident rate for all incidents and also those classified as serious categorized by the years of bicycling experience for the respondents.

City Size and Topography

Figures 17 and 18 show what the accident rates were for respondents living in different size cities and also riding in different types of terrain. There appears to be no major differences for accident occurrence in different size cities, although there is a slightly lower rate for both the cases of all accidents and serious accidents in smaller cities than larger cities.

Location of Crash and Trip Purpose

Table 13 permits comparisons to be made for accidents that occurred on different type facilities, ranging from major streets to separate bicycle paths. Similarly, Table 14 provides information as to the trip purpose or activity underway at the time of the crash. Off-street bicycle facilities (that do not allow motor vehicle traffic) showed the highest overall accident rate, and also an extremely high serious accident rate. In fact, the serious accident rate of 79.6 incidents per million bicycle miles traveled was the highest calculated rate for any analysis done in the study. On an accident frequency basis, a L.A.W. bicyclist riding on off-street bikeways would likely be involved in a serious collision or fall requiring professional medical treatment once every 12,600 miles, or every five and one-half years, a much higher frequency than any other facility studied. No explanation is known for this finding. A guess might be that cyclists use less caution on this type facility, feeling it is free of the menacing motor vehicle only to collide with a tree or fall on some slippery gravel. Coincidentally, the lowest accident rate existed for both the categories of all accidents and serious accidents when those incidents that occurred on bikelanes and bike routes were examined. As expected, the rate for accidents occurring on minor streets was somewhat lower than those incidents occurring on major streets. This is probably due to less exposure to high speed and/or high volume traffic for the bicyclist when using minor streets compared to travel on major streets.

TABLE 13

ACCIDENT RATE BY LOCATION OF CRASH

TABLE 14 - ACCIDENT RATE BY TRIP PURPOSE

When the relationship between trip purpose and accidents is examined, the utility trip stands out as having the highest rate of incidents, both for serious accidents and also when all accidents are studied. The commute trip (work or school) had the lowest rate in both categories of accidents. This latter finding may have occurred because a person making regular trips over the same route on an almost daily basis learns the "reel" of the route, and its bad sections and good sections. Similar to a truck driver using precautions when he is on a certain section of a familiar road, this acquired skill in "reading" the road from repetitious use allows the cyclist to travel safer, and thereby reduce his accident potential.

Responses to Safety-Related Questions

An attempt was made to determine if the respondent's attitude toward safety and obeyance of the law had any effect on his accident involvement.

Figure 19 shows the accident rate of those respondents who stated that they wore a helmet and used a rear view mirror while riding a bicycle, and those that did not.

Respondents who answered that they "occasionally" obeyed vehicle laws while riding their bicycles had an accident rate 38 percent higher than those that "usually" and "always" obeyed the laws. Also, the serious accident rate was higher for these individuals. This subjective question was added to the questionnaire with the intent of obtaining a general idea of what regular bicycle users felt toward the vehicle laws as they applied to bicycles. (more discussion on this subject can be found in the section "Attitudinal Questions" in Chapter IV.) However, some very interesting findings have also appeared with regard to the relationship between accident involvement and how the respondent feels toward obeyance of the law.

Responses to Ride in Rain and in the Dark Questions

Table 15 shows the results when accident rates are computed for both categories of all accidents and serious incidents only, stratified by how often the respondent rode a bicycle after dark or in the rain. Interestingly, in both cases, the rider who stated he bicycled in what seemingly would be considered more accident producing conditions, showed lower accident involvement rates. This relationship appears to hold true for both the rates involving all accidents and the more serious incidents requiring professional medical treatment. A possible explanation may be that the respondents who ride at night and in the rain realize the more dangerous conditions and bicycle accordingly.

TABLE 15

ACCIDENT RATE BY RESPONSE TO RIDE IN RAIN AND DARK QUESTIONS
PER MILLION BICYCLE MILES TRAVELED

Comparison with Auto Accident Rate

In order to put into perspective the bicycle accident rates that have been discussed in this report, motor vehicle accident rates available from the Federal Highway Administration are presented for comparison (17). For the year 1973 (the latest year data are available), the overall non-fatal injury rate shows that about 2.4 such injuries occur in one million miles of driving on all non-Interstate highways. This rate rises to 2.9 when only urban rates are examined. These injuries are defined as any bodily harm received by any person in a motor vehicle traffic accident, including pedestrians and bicyclists. It is assumed, however, that only injuries resulting from a serious enough accident requiring police to file a report would be the type entered into these rate calculations.

Assuming that any bicycle injury requiring at least a doctor visit or emergency room treatment would be an equivalent type Injury, the bicycle rate of 31.4 accidents per million bicycle miles traveled is the comparable rate. It should be remembered that an automobile is driven an average of 9,992 miles a year (23), while the bicyclists in this survey averaged 2,232 miles a year, only about one-fifth as much. Even with this adjustment, the bicycle accident injury rate in this study was about twice as high as the motor vehicle traffic accident injury rate.

To put these accident rates in perspective, it should be remembered that these rates are equivalent to a moderate or serious incident once every 14 years for a bicyclist, and approximately once every 28 years for a motorist, or anyone involved in a motor vehicle traffic accident.