Journal of Community Health

, Volume 41, Issue 6, pp 1160–1166 | Cite as

The Effect of an All-Ages Bicycle Helmet Law on Bicycle-Related Trauma

  • Paula Kett
  • Frederick Rivara
  • Anthony Gomez
  • Annie Phare Kirk
  • Christina Yantsides
Original Paper

Abstract

In 2003, Seattle implemented an all-ages bicycle helmet law; King County outside of Seattle had implemented a similar law since 1994. For the period 2000–2010, the effect of the helmet legislation on helmet use, helmet-preventable injuries, and bicycle-related fatalities was examined, comparing Seattle to the rest of King County. Data was retrieved from the Washington State Trauma Registry and the King County Medical Examiner. Results comparing the proportions of bicycle related head injuries before (2000–2002) and after (2004–2010) the law show no significant change in the proportion of bicyclists admitted to the hospital and treated for head injuries in either Seattle (37.9 vs 40.2 % p = 0.75) nor in the rest of King County (30.7 vs 31.4 %, p = 0.84) with the extension of the helmet law to Seattle in 2003. However, bicycle-related major head trauma as a proportion of all bicycle-related head trauma did decrease significantly in Seattle (83.9 vs 64.9 %, p = 0.04), while there was no significant change in King County (64.4 vs 57.6 %, p = 0.41). While the results do not show an overall decrease in head injuries, they do reveal a decrease in the severity of head injuries, as well as bicycle-related fatalities, suggesting that the helmet legislation was effective in reducing severe disability and death, contributing to injury prevention in Seattle and King County. The promotion of helmet use through an all ages helmet law is a vital preventative strategy for reducing major bicycle-related head trauma.

Keywords

Bicycle injury Head injury Major head injury Helmet Legislation 

Introduction

While bicycling in the United States has not always been as popular as it is today, it has steadily increased in the past 30 years for both recreational and commuter purposes. A review of the literature examining the specific health benefits of bicycling reveals a positive dose–response relationship between bicycling and health benefits, particularly cardio-respiratory fitness in youth [1]. In addition, studies show an inverse relationship between bicycling and all-cause mortality, cancer mortality and morbidity, and obesity [2]. Other benefits of bicycling include reduced risk for colon cancer and diabetes, improved balance, and reduced risk of falls [3, 4]. In addition to health benefits for the rider, a modal shift from cars to bicycles has the added environmental and societal benefit of reduction in traffic congestion and carbon monoxide emissions [1]. Public Bicycle Share Programs (PBSP) are increasing in popularity in North American cities, including Seattle, and have contributed to the popularity of bicycling as a means of transportation [5]. A recent study on PBSP and head injuries found that PBSP implementation is associated with an increased risk of bicycle related head injuries. These findings further support the importance of public safety by promoting helmet use and necessity of an all-ages helmet law.

While bicycling is important for health, it does carry inherent risks of injury, particularly traumatic brain injury (TBI). According to the National Highway and Traffic Safety Administration (NHTSA), there were approximately 51,000 bicycle injuries and 630 bicycle-related deaths in 2010 in the United States [6]. Nationally, TBI is the leading cause of bicycle-related death and disability [7, 8]. Since the mid-1990’s, studies have demonstrated the effectiveness of bicycle helmets to reduce bicycle-related head and brain injuries, showing that riders who wore helmets had an 85 % reduction in risk of head injury and an 88 % reduction in risk of brain injury [9, 10, 11].

Helmet legislation plays an important role in reducing preventable and decreasing the severity of TBI, as policy change is a crucial component in a comprehensive model of prevention. Such legislation, once implemented, has been shown to be effective in both increasing helmet use and reducing bicycle-related head injuries [12, 13, 14, 15]. The effect is especially large for increasing helmet use where the law applied to all ages, versus only to children under the age of 16 [16, 17]. For areas with helmet laws restricted to children, no study has shown a spillover effect to adult helmet use [16]. Prior studies have found up to a 60 % reduction in bicycle-related fatalities for the populations in which legislation is implemented [7, 15, 18, 19]. A majority of these studies examined helmet laws for children; however, a recent study in Australia examining their all-ages law found a positive effect on bicycle-related head injuries at the population level [20] In the US, 58 cities and counties have all-ages helmet legislation in place; 22 states have compulsory helmet laws, although none apply to all ages.

Much controversy surrounds the implementation of helmet laws, with opponents citing potential unintended consequences, including reduced ridership, promotion of the belief that bicycling is a “dangerous” activity, increased risk-taking behavior, and diversion of resources away from infrastructure improvements. While not a consequence of a helmet law, others believe there is still a lack of solid evidence documenting the effectiveness of helmets in preventing bicycle-related head injury and so do not advocate for such legislation [1, 21]. However, as can be seen by the evidence presented above, as well as numerous other studies, these arguments are flawed and have little quality evidence to support them [22, 23, 24, 25]. Moreover, a recent study in Canada examining ridership before and after legislation found no significant change in recreational and commuting bicycle use [13], and no studies have been published showing that helmet promotion or helmet laws have reduced bicycling in any community within the US, or that helmet use leads to an increase in injuries.

Most studies of helmet laws only examine legislation requiring helmets for youth ≤18 years of age. This paper proposes to fill this gap, examining the reduction in helmet-preventable injuries since all-ages helmet legislation went into effect in Seattle in 2003 and comparing this data to the rest of King County outside of Seattle, where legislation has been in effect since 1994.

Methods

King County is the most populous county in Washington State and the 14th most populous in the United States; it is home to approximately 1.9 million people. The county seat is the city of Seattle, which is the largest city in Washington State. In 2003, a compulsory, all-ages bike helmet law was implemented in Seattle; prior to this, in 1994, the King County Board of Health (BOH) had instituted a compulsory all-ages helmet law, but Seattle was not included in this regulation since at that time Seattle had a separate BOH. Key themes in this successful effort included garnering widespread community and agency support through presenting evidence of helmet effectiveness, summaries of bicycle injury and death cases that could have been prevented with helmet use, and the medical and fiscal costs of helmet-preventable injuries. In addition, evidence indicates that to maximize children’s use of a safety device, such as wearing helmets and seatbelts, it is important for adults to model this behavior [26].

Major aspects of successfully implementing this legislation included increasing awareness through the use of a health educator, partnering with low-cost helmet providers to increase access, and participating in extensive discussions with key community stakeholders, including the Seattle Police Department (SPD), Seattle Public Schools, Seattle Fire Department, Seattle Children’s Hospital, and regional bicycle clubs. Investigation into how a Board of Health ruling could be enforced by police also took place. This resulted in unanimous passage of the new helmet regulation to include Seattle with the rest of King County.

Data Collection

Data was obtained from the Washington State Trauma Registry, which includes all injured individuals who were admitted to a Level I-V trauma center for 24 h or longer. Information on trauma fatalities, regardless of location of death, was collected from the Medical Examiner. All bicyclist trauma which took place within King County was included, based on the home zip code locations of the trauma victims. Data from King County excluded Seattle data in order to examine the effect of the law in Seattle; data from Seattle was collected and defined in the same way as for King County. All injuries involving bicycles were included as part of the analysis; incidence of bicycling injuries were examined by age, as well as by occurrence of head injury and severity of head injury. Head injuries were defined by the following ICD-9 codes: 800–801.9, 803–804.9, 850–854, 873–873.1. Major TBI injuries were those with an Abbreviated Injury Scale (AIS) score ≥3. Criteria for inclusion in this analysis was an injury coded as a TBI injury (based on the ICD-9 code) and coded as a major injury (≥3 AIS) or minor injury (AIS <3).

Seattle and King County population estimates were from the Washington State Department of Health (WA DOH), Population Estimates for Public Health Assessment and retrieved by the Assessment, Policy Development, and Evaluation Unit (APDE), Public Health – Seattle & King County.

The proportions of bicyclist trauma were calculated based on the number of total trauma patients admitted for each year from 2000 to 2010. The proportions of bicyclist trauma involving a head injury were calculated based on the total number of bicyclist trauma patients admitted for each year from 2000 to 2010. This data was further stratified by gender and age—those younger than 18 years and those 18 years and older. Data from the trauma registry was analyzed using STATA 11 and trends were examined for significance (p < 0.05) using the JoinPoint Regression Program, Version 3.5.

Population estimates for the years 2000–2010 were used to calculate incidence of injuries per 100,000 population. Incidence rates for bicycle-related trauma and those resulting in no, minor (1 < AIS < 3), or major (≥3 AIS) head trauma were calculated separately for adults, children under 18, and the total population for each year 2000–2010. Incidence rate ratios were used to compare incidence rates before (2000–2002) and after (2004–2010) the updated helmet law was instituted for adults and children in each category of trauma. Statistical testing was performed for the hypothesis that no difference was present in incidence rates before and after the helmet law.

An odds ratio was calculated to estimate the association between helmet use and head trauma among people experiencing any bicycle-related trauma. Incidence rate ratios, odds ratios, confidence intervals, and p-values were calculated using Stata version 12 (StataCorp LLC, College Station, TX). Proportions for pre- and post-helmet law periods were tested for statistical significance using the univariate Chi-square test. It was determined a priori that two-sided p values ≤0.05 would be considered statistically significant. Since only de-identified data was used, the study was exempt from IRB review.

Results

There were a total of 767 injured bicyclists in King County (not including Seattle) from 2000 to 2010, accounting for 3.2 % of all admitted trauma patients in King County during that time. During this same time period, there were 547 injured bicyclists in Seattle, accounting for 3.8 % of all admitted trauma patients in Seattle. Among those involved in a bicycle-related trauma, the proportion of helmet-wearers in King County increased from 26 % (n = 13) to 60 % (n = 61), while the proportion in Seattle increased from 39 % (n = 13) to 68 % (n = 49) over the period 2000–2010.

During this time, the incidence in bicyclist trauma increased in both Seattle (2.8–5.4 per 100,000) and King County (4.2–7.7 per 100,000). Among all bicyclist trauma patients in King County during this time period, 226 (29 %) involved head injuries, 138 (18 %) of which were major head injuries (Table 1). During this same time period, 213 (39 %) of all bicyclist trauma patients in Seattle involved head injuries, 144 (26 %) of which were major head injuries (Table 2).
Table 1

King County (excluding Seattle) bicyclist trauma, 2000–2010

Year

Total population

Total trauma

All bicycle trauma

Bicycle head trauma

Bicycle major head trauma

(n)

Incidence per 100,000

(%) of all trauma

(n)

Incidence per 100,000

(%) of all trauma

(%) of Bicyclist trauma

(n)

Incidence per 100,000

(%) of all trauma

(%) of Bicyclist trauma

% of head traumas

2000

1,173,661

1703

49

4.2

2.9

15

1.3

0.9

31

10

0.85

0.59

20.4

67

2001

1,188,491

1784

45

3.8

2.5

11

0.9

0.6

24

6

0.50

0.34

13.3

55

2002

1,203,368

1713

59

4.9

3.4

19

1.6

1.1

32

13

1.08

0.76

22.0

68

2003

1,218,245

1786

67

5.5

3.8

24

2.0

1.3

36

18

1.48

1.01

26.9

75

2004

1,233,123

1809

59

4.8

3.3

11

0.9

0.6

19

6

0.49

0.33

10.2

55

2005

1,248,000

2333

72

5.8

3.1

24

1.9

1.0

33

16

1.28

0.69

22.2

67

2006

1,262,878

2303

67

5.3

2.9

24

1.9

1.0

36

17

1.35

0.74

25.4

71

2007

1,277,756

2537

78

6.1

3.1

21

1.6

0.8

27

14

1.10

0.55

17.9

67

2008

1,292,632

2741

82

6.3

3.0

22

1.7

0.8

27

17

1.32

0.62

20.7

77

2009

1,307,510

2872

87

6.7

3.0

20

1.5

0.7

23

10

0.76

0.35

11.5

50

2010

1,322,388

2970

102

7.7

3.4

35

2.6

1.2

34

11

0.83

0.37

10.8

31

Totals

767

226

138

Table 2

Seattle bicyclist trauma, 2000–2010

Year

Total population

Total trauma

All bicycle trauma

Bicycle head trauma

Bicycle major head trauma

(n)

Incidence per 100,000

(%) of all trauma

(n)

Incidence per 100,000

(%) of all trauma

(%) of Bicyclist trauma

(n)

Incidence per 100,000 population

(%) of all trauma

% of Bicyclist trauma

% of head traumas

2000

563,383

1008

33

2.8

3.3

10

0.85

1.0

30

10

0.85

1.0

30

100

2001

567,957

945

18

1.5

1.9

9

0.76

1.0

50

8

0.67

0.8

44

89

2002

572,493

1159

36

3.0

3.1

12

1.00

1.0

33

8

0.66

0.7

22

67

2003

577,029

1120

44

3.6

3.9

17

1.40

1.5

39

11

0.90

1.0

25

65

2004

581,565

1222

37

3.0

3.0

9

0.73

0.7

24

6

0.49

0.5

16

67

2005

586,101

1387

53

4.2

3.8

20

1.60

1.4

38

15

1.20

1.1

28

75

2006

590,637

1470

41

3.2

2.8

17

1.35

1.2

44

10

0.79

0.7

24

59

2007

595,173

1673

83

6.5

5.0

32

2.50

1.9

39

23

1.80

1.4

28

72

2008

599,709

1584

71

5.5

4.5

32

2.48

2.0

45

18

1.39

1.1

25

56

2009

604,245

1513

59

4.5

3.9

28

2.14

1.9

47

20

1.53

1.3

34

71

2010

608,781

1398

72

5.4

5.2

27

2.04

1.9

38

15

1.13

1.1

21

56

Totals

547

213

144

The proportion of bicyclist trauma in King County involving head injuries increased from 31 % in 2000 to 36 % in 2006 and then decreased to 34 % in 2010 (Table 1; Fig. 1). In Seattle, the proportion of bicyclist trauma involving a head injury increased from 30 % in 2000 to a peak of 50 % in 2001, decreasing in 2010 to 38 % of all bicyclist trauma (Table 2; Fig. 2). Comparing the time periods of 2000–2002 and 2004–2010, there was no significant change in the proportion of cyclists with head injuries in either Seattle (35.6 vs 39.7 %, p = 0.48) or in King County (29.4 vs 28.7 %, p = 0.90) with the extension of the helmet law to Seattle in 2003. Similarly, major head trauma as a proportion of all bicycle trauma did not change significantly in either Seattle (29.9 vs 25.7 %, p = 0.42) or in King County (19.0 vs 16.6 %, p = 0.50). However, major head trauma as a proportion of bicycle-related head trauma did decrease significantly in Seattle (83.9 vs 64.9 %, p = 0.04) but did not change significantly in King County (64.4 vs 58.0 %, p = 0.41).
Fig. 1

Seattle and King County, incidence of bicycle-related trauma per 100,000 population, <18 years, 2000–2010

Fig. 2

Seattle and King County, incidence of bicycle-related trauma per 100,000 population, 18+ years, 2000–2010

After the helmet law was extended to include Seattle, the absolute population-based incidence of bicycle related head trauma increased in Seattle [incidence rate ratio (IRR) of 2004–2010 compared with 2000–2002 was 2.18, 95 % CI 1.48, 3.31], which was a larger increase in incidence than in King County over this same time period (IRR 1.40, 95 % CI 1.00, 2.00). Age-specific data showed no significant change in bicycle-related head trauma for those under 18 in either Seattle (IRR 1.15, 95 % CI 0.52, 2.79) or in King County (IRR 1.04, 95 % CI .65, 1.70). For those 18 years and older, there was a significant increase in bicycle-related head trauma in both Seattle (IRR 2.60, 95 % CI 1.65, 4.28) and in King County (IRR 2.11, 95 % CI 1.28, 3.65).

In King County, including Seattle, there were a total of 35 bicycle-related fatalities from 2000 to 2010. Prior to the implementation of the helmet law, there were an average of 4.7 fatalities per year; this decreased to an average of 3 fatalities per year after the law was implemented. Of the 35 fatalities, 28 involved a motor vehicle. Of the 7 that did not involve a motor vehicle, 6 were not wearing a helmet and the cause of death was TBI. Of the one bicycle fatality where the user was wearing a helmet and the trauma did not involve a motor vehicle, the cause of death was not a TBI. It was previously found in the King County Child Fatality Review (CFR) process that between 1998 and 2002, 5 children died while riding bicycles. It was determined by the CFR expert committee that of the 4 children not wearing helmets, 3 of them would have lived had a helmet been worn. There have been no bicycle-related (helmet preventable) fatalities for those under age 18 since 2005.

Discussion

The results demonstrate a decrease in the severity of bicycle-related TBI since implementation of the law, as well as a decrease in the number of fatalities, including child deaths, showing that implementation of the helmet legislation may have contributed significantly to injury prevention in Seattle and throughout King County. Furthermore, this is supported by our data and field observations from the Seattle Department of Transportation (SDOT) which have observed that more bicyclists are wearing helmets since the implementation of the 2003 all-ages helmet law.

Our data indicates that the number of injured bicyclists wearing helmets has increased since the implementation of the all-ages helmet law in 2003. However, there has also been an increase in the incidence of bicycle-related trauma and bicycle-related trauma involving head injuries, although there has been a decrease in the proportion of riders with major head injuries. This suggests that the helmet law may have been effective in decreasing the severity of head injuries sustained and thus prevented severe disability and death.

Since the helmet legislation was implemented, bicyclist injuries for those under 18 have not increased while the incidence of bicycle-related trauma in adults has increased, suggesting a protective effect of helmet legislation in reducing head injuries and fatalities in those under 18. As previous studies have shown, modeling behavior is important in successfully getting children to adopt health-promoting behavior. Thus, helmet legislation for all-ages is important in ensuring those under 18 continue to wear helmets.

While data is not available for ridership and helmet use for the entire City or County, there is an increase in the incidence of all bicycle-related trauma, which likely indicates an increase in ridership. It is unlikely that this increase in trauma is due to an increase in injuries per rider as, in addition to the helmet legislation, there have been environmental and infrastructure changes implemented in both Seattle and King County aimed at encouraging bicycling as well as increasing bicycle safety. Moreover, enforcement of the helmet law in Seattle by police has increased from 11 tickets written in 2003 to 447 tickets in 2011 [27]. These data suggest that the enforced all ages helmet law does not likely reduce ridership.

Limitations

While this study had data from the regional trauma centers in King County, there was no data on miles traveled by bicyclists or other exposure methods. In addition, while the number of bicyclists treated at the trauma centers has increased, there is no comprehensive data with an actual number of regular bicyclists in Seattle and in King County.

Conclusion

In 2003, when King County’s comprehensive helmet legislation was expanded to include Seattle, it was inferred that the helmet law would lead to decreased bicycle-related head trauma. Data from the trauma registry has confirmed this presentation, indicating that the law was associated with a decrease in major and fatal head trauma. In addition, it appears that the legislation did increase helmet use, which corroborates with what similar studies found [19]. In the future, in order to better gauge the effect of helmet legislation, it’s essential to have consistent data collection, such as looking at bicycle miles traveled, in order to measure exposure. The population of bicyclists is expected to increase with climate change and a continued focus on population health and having healthier communities. Bike shares are quickly becoming more and more popular, making helmet availability and education for bike share users a pressing need.

Notes

Acknowledgments

We would like to thank the following individuals for their contributions to this paper: Kathy Schmidt, Zeynep Shorter, Wren Haaland, and Nick Zajchowski.

Statement of Contributorship

Paula Kett acquired and analyzed the data and produced the manuscript. Frederick Rivara, Tony Gomez, Annie Phare Kirk and Christina Yantsides assisted in the conception and design of the manuscript. All authors read, revised, and gave final approval of the manuscript.

Compliance with Ethical Standards

Conflict of interest

The authors declare they have no conflict of interest.

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Copyright information

© Springer Science+Business Media New York 2016

Authors and Affiliations

  • Paula Kett
    • 1
  • Frederick Rivara
    • 2
  • Anthony Gomez
    • 1
  • Annie Phare Kirk
    • 1
  • Christina Yantsides
    • 1
  1. 1.Public Health – Seattle & King CountySeattleUSA
  2. 2.Department of Pediatrics and Harborview Injury Prevention and Research CenterUniversity of WashingtonSeattleUSA

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