Motor Vehicle Fatalities during Memorial Day Weekends, 1981-2016

doi:10.21203/rs.2.16680/v1

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Motor Vehicle Fatalities during Memorial Day Weekends, 1981-2016

https://doi.org/10.21203/rs.2.16680/v1

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published 03 Jan, 2020

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Objective: Our aims were to determine which day(s) during the holiday had highest motor vehicle fatality risk compared to non-holiday travel and to identify potential risk factors. Results: Of 43,457 traffic fatalities studied, 15,292 (35%) occurred during the holiday, with Saturday being deadliest but Monday having highest odds. Both sexes, all years, age <65, drivers and passengers, rural and urban, and all regions in the United States were at increased risk during the holiday versus non-holiday periods.

Health Economics and Outcomes Research

Motor vehicle crash

Fatalities

Memorial Day

Fatality Analysis Reporting System (FARS)

Binomial approximation

Motor vehicle crashes are a major concern in the United States, with more than 37,000 people killed in 2016, and an increase of nearly 2,000 fatalities from 2015 to 2016 [1]. There were 36,560 highway fatalities in 2018, with a decreased 918 fatalities from 2017 to 2018 [2]. Motor vehicle crashes cost an estimated $18 billion in lifetime medical expenses and $33 billion in lifetime work lost in 2012 [3]. Thus, there is an urgent need to improve traffic issues to make roads safer for all road users.

Holidays are times of increased road travel. In 2003, the number of long-distance trips during holiday periods in the United States were higher than the average number for the rest of the year, and motor vehicle is one of the most popular modes of private recreational travel during the holidays in the United States [4]. Memorial Day is a national holiday in the United States occurring the last Monday in May, with the holiday weekend beginning on the preceding Saturday marking the unofficial start of the summer travel season. The Missouri State Highway Patrol found that Memorial Day is one of six holidays with increased traffic crashes [5]. Another report compared injuries and fatalities across six holidays from 1982 to 2001 [6], Memorial Day had the third highest number of fatal crashes. However, neither study compared holiday to non-holiday crashes.

The primary aim of our study was to evaluate the risk of a fatal motor vehicle crash during the Memorial Day weekend and to determine which day(s) had the highest risk. Our second aim was to identify possible risk factors associated with odds of motor vehicle fatality during the Memorial Day weekend.

The National Highway Traffic Safety Administration (NHTSA)‘s Fatality Analysis Reporting System (FARS) is a national census of fatal traffic crashes in the United States [7]. We used a 1:2 case-control study using time-referenced definition for cases and controls (1981–2016). This study design has been used previously to analyze FARS data [8–12]. The design can adjust for the variation of seasonality and daytime and provide an epidemiologic method for controlling for unmeasured confounders (e.g.: drivers’ education and drive licenses status).

Cases were defined as fatalities occurring during the Memorial Day holiday (Saturday through Monday). Controls were the corresponding 72 hours precisely one week before and after the holiday. Seven factors were selected for analysis including day of week (Saturday, Sunday, Monday), year groups (5-year group from 1981 to 2010, the final group had 6 years), age (<18 years old, 18–64 years old, ≥ 65 years old), sex (male, female), role (driver, passenger, pedestrian/other), census region (Midwest, Northeast, South, West), and road location (rural, urban).

Descriptive analysis used Chi-square to compare holiday vs. control fatality counts and percentages. We evaluated odds of holiday fatality using a binomial approximation. In essence, the averaged control fatalities represent the expected traffic fatalities during non-holiday periods, and the holidays are the observed fatalities of interest. By dividing the observed by expected fatalities, an odds ratio (OR) and 95% confidence intervals (CI) can be calculated to estimate risk. An assumed non-eventful driving exposure of one million was used for all study days [10]. All the analysis were conducted using SAS version 9.4 (SAS Institute, Cary, NC). The statistical significance was defined as p<0.05.

From 1981–2016, 43,557 fatalities occurred during the 3-day Memorial Day weekend (n = 15,292; 35%) and six corresponding control days. The average number of deaths per day during the holiday was 142, compared to 132 the week before (n = 14,293) and 128 the week after (n = 13,772). For the holiday, Saturday had the highest number of fatalities (n = 6,053; 40%) while Monday (Memorial Day) had the lowest (n = 4,104; 26%) (Table 1).. By year group, 1986–1990 had the highest holiday fatality count (n = 2,466; 16%) and 2006–2010 had the lowest (n = 1,998; 13%), but overall counts were stable over time. The majority of fatalities for both holiday and control periods were adults and males. During the holiday, 11,745 (77%) of fatalities were adults and 10,879 (71%) were males. Most fatalities during Memorial Day weekend were drivers (n = 8,971; 59%). Fatality counts were highest in the South (n = 6,692; 44%). More fatalities during each period occurred in urban than rural areas (n = 13,066; 85% vs. n = 2,148; 15%). The odds of a motor vehicle fatality occurring during Memorial Day weekend were 9% greater than during the control periods (OR:1.09, 95% CI: 1.07–1.12) (Table 2 and Figure 1).. Compared to the control periods, the odds of fatality on Memorial Day was 18% higher (OR: 1.18, 95% CI: 1.12–1.23), and 8% greater on the holiday Saturday (OR: 1.08, 95% CI: 1.04–1.12). Analysis of 5-year categories showed they all had increased odds of fatality during Memorial Day weekend compared to control days.

Table 1. Characteristics of Individuals Involved in Fatal Crashes during the Memorial Day Weekends

Table 2. Odds Ratio and 95% CI for Motor Vehicle Fatalities during Memorial Day Weekends

Figure 1. Odds Ratio and 95% CI for Motor Vehicle Fatalities during Memorial Day Weekends

^†This forest plot shows US motor vehicle fatalities from 1981 to 2016. The right side of the forest plot shows a relative increase in risk on Memorial Day weekends compared to control days computed as odds ratio using the averaged count of control fatalities as the referent group. The left side of the forest plot shows all the subgroups of fatalities. Column numbers are fatality counts. Odds ratios greater than 1.00 show an increased risk of crash-related deaths during holiday periods compared to non-holidays, and confidence intervals excluding 1.00 are considered statistically significant at p<0.05.

Odds of traffic fatalities differed by demographics. Adults aged 18–64 experienced 11% higher odds (OR: 1.11, 95% CI: 1.08–1.14) and individual younger than 18 and 10% higher odds of traffic fatalities during the Memorial Day weekend (OR: 1.10, 95% CI: 1.03–1.18). Females had 10% increased odds (OR: 1.10, 95% CI: 1.05–1.15), and males had 9% increased odds of crash-related fatalities during Memorial Day weekend compared to control days (OR: 1.09; 95% CI: 1.06–1.12). Odds of holiday traffic fatalities also differed by role with passengers 17% more likely (OR: 1.23, 95% CI: 1.18–1.29) and drivers 5% more likely (or: 1.05; 95% CI: 1.02–1.08).

Geographically, people in the Northeast experienced 16% increased odds of fatality during the Memorial Day weekend compared with control days (OR: 1.16, 95% CI: 1.09–1.24). Regarding the crash location, the odds of the fatality on rural areas had 14% greater than the control days (OR: 1.14, 95% CI: 1.07–1.21), and an 8% increase in urban areas (OR: 1.08, 95% CI: 1.06–1.11).

As expected, due to increased traffic volume and longer travel distances during holidays, holiday travel had higher odds of traffic fatality compared to non-holiday periods. Saturday was the deadliest day overall, as well as for holiday and control periods, although Memorial Day Monday had the highest odds of holiday fatality compared to control periods and the odds on Sunday were only marginally significant. Additionally, the increased travel during holidays can explain higher risk of holiday traffic deaths among adults and children (individuals younger than 18). The higher odds of crash-related deaths during holiday periods might reflect children and their families travelling together for longer distances compared to typical work and school commutes. Public campaigns need to make efforts to remind drivers to expect increased congestions and delays during holidays.

Nearly every category we analyzed had increased odds of a holiday traffic fatality, indicating that Memorial Day holiday travel patterns compared to typical travel are not isolated to certain demographic or geographic characteristics. The majority of motor vehicle crash fatalities were in urban areas during both holiday and control days likely due to nearly eighty percent of the U.S. population residing in urban areas [13, 14]. However, rural areas had higher risk of a holiday traffic fatality compared to control days. This may suggest that motor vehicle crashes in rural areas were over-represented during public holidays [15]. Higher risk of traffic fatality in rural areas can reflect increased long-distance travel in these areas during holidays [15, 16].

A holiday, including Memorial Day weekend, is a chance to take off work pressure and enjoy time with friends and family members. Unfortunately, holidays are also associated with increased risky behaviors, such as drinking and other inappropriate driving behaviors [17]. One traffic safety measure is the use of sobriety checkpoints in selected locations to reduce the risk of alcohol-related traffic deaths. However, one study showed that crash fatalities with higher BAC threshold remained stable on holidays despite a campaign of targeted enforcement to address the dangers of alcohol-involved driving [18].

The strength of our study was our use of a national census of all crash-related fatalities on public roadways from 1981 to 2016 with comprehensive information for all eligible fatal crashes. We also used an established method of comparing a case period with corresponding double control periods. This method can eliminate multiple unmeasured confounders, clarifies interpretation, and avoids misunderstanding.

In our study, most of the factors with the increased risk during the holiday are the reflection of presumed increased exposure, such as increased holiday travel by distance, time, and increased traffic volume. Therefore, public campaigns are needed to improve road safety of all road users and focus on reminding travelers to expect delays and increased congestion.

The main limitation of our study is that FARS dataset lacks holiday-specific travel exposure data (miles or time travelled) to conduct day-specific traffic fatality analysis, limiting our ability to pinpoint the causes for increased odds of holiday traffic fatalities.

Ethics approval and consent to participate

No applicable.

Consent for publication

No applicable.

Availability of data and materials

The FARS dataset was derived from the Internet, at ftp://ftp.nhtsa.dot.gov/FARS and may also be accessed on the web at www-fars.nhtsa.dot.gov. The derived data are made available with the article.

Competing interests

The authors declare that they have no competing interests.

Funding

This research was supported by the National Institute of Health [R01HD074594, 2013–2022; R01AG050581, 2015–2020]. The funding sources had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Author’s contributions

Y. T., H. X., and M. Z. conceived the idea for the study. Y. T. and K. L. R. designed the study. Y. T. carried out the analysis and K. L.R validated results. All authors interpreted data. Y. T. wrote the first draft of the article, with critical revisions by K. L. R., H. X., and M. Z. All authors commented on and approved the final manuscript.

Acknowledgements

Not applicable.

NHTSA, 2017[a]. 2016 fatal motor vehicle crashes: overview. National Centre for Statistics and Analysis. No. DOT HS 812 456. October 2017. Accessed October 2017. Retrived from: https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/812456
NHTSA, 2018. 2018 fatal motor vehicle crashes: overview. National Centre for Statistics and Analysis. No. DOT HS 812 456. October 2017. Accessed October 2019. Retrived from: https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/812826
2014. CDC report shows motor vehicle crash injuries are frequent and costly. Retrieved from: https://www.cdc.gov/media/releases/2014/p1007-crash-injuries.html Accessed 7 October 2014.
BTS, 2003. U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics: America on the go: U.S. holiday travel. Retrieved from:

https://www.bts.gov/sites/bts.dot.gov/files/legacy/publications/america_on_the_go/us_holiday_travel/pdf/entire.pdf.

MSHPSAC, 2003. Missouri Holiday Crashes Report. Missouri State Highway Patrol Statistical Analysis Center, Jefferson City.
NHTSA, 2004. Times series analysis and forecast of crash fatalities during six holiday periods. National Center for Statistics and Analysis. DOT HS 809 718. March 2004. Retrieved from: https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/809718
NHTSA, 2017[b]. Fatality Analysis Reporting System (FARS) Analytical User’s Manual 1975-2016. National Highway Traffic Safety Administration. DOT HS 812 447. Washington. DC. Accessed October 2017.
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Table 1. Characteristics of Individuals Involved in Fatal Crashes during the Memorial Day Weekends

	N (%)¹
	Holiday Period	Control Days	P-value ²
	15,292 (35)	28,065 (65)
Day of week			<.001
Saturday	6,053 (40)	11,222 (40)
Sunday	5,135 (34)	9,882 (35)
Monday	4,104 (26)	6,961 (25)
Year groups ³			<.001
1981-1985	2,299 (15)	4,309 (15)
1986-1990	2,466 (16)	4,560 (16)
1991-1995	2,079 (14)	3,865 (14)
1996-2000	2,090 (14)	3,871 (14)
2001-2005	2,238 (15)	4,019 (14)
2006-2010	1,998 (13)	3,614 (13)
2011-2016	2,122 (14)	3,827 (14)
Age			<.001
<18 y	1,885 (12)	3,425 (12)
18-64 y	11,745 (77)	21,215 (76)
>65 y	1,662 (11)	3,425 (12)
Sex			<.001
Male	10,879 (71)	20,011 (71)
Female	4,405 (29)	8,023 (29)
Unknown/Not reported	8	31
Role			<.001
Driver	8,971 (59)	17,087 (61)
Passenger	4,453 (29)	7,214 (26)
Pedestrian/Other	1,868 (12)	3,764 (13)
Region			<.001
Midwest	3,327 (21)	6,030 (21)
Northeast	2,057 (13)	3,544 (13)
South	6,692 (44)	12,523 (45)
West	3,216 (21)	5,968 (21)
Location			<.001
Rural	2,148 (14)	3,768 (13)
Urban	13,066 (85)	24,136 (86)
Unknown	78	161

¹ Missing values and unknowns are not represented in the percentages.

² The statistical significance was defined as p<0.05.

³The year group of “2011-2016” has 6 rather than 5 years.

Table 2. Odds Ratio and 95% CI for Motor Vehicle Fatalities during Memorial Day Weekends

	OR^*	95% CI^*	p-value ¹
Total fatalities	1.09	1.07, 1.12	<0.001
Day of week
Saturday	1.08	1.04, 1.12	<0.001
Sunday	1.04	1.00, 1.08	0.05²
Monday	1.18	1.13, 1.23	<0.001
Year groups
1981-1985	1.07	1.01, 1.13	0.030
1986-1990	1.08	1.02, 1.15	0.007
1991-1995	1.08	1.01, 1.14	0.021
1996-2000	1.08	1.02, 1.15	0.015
2001-2005	1.11	1.05, 1.18	0.001
2006-2010	1.11	1.04, 1.18	0.002
2011-2016 ³	1.11	1.04, 1.18	0.001
Age
<18 y	1.10	1.03, 1.18	0.004
18-64 y	1.11	1.08, 1.14	<0.001
>65 y	0.97	0.91, 1.04	0.385
Sex
Male	1.09	1.06, 1.12	<0.001
Female	1.10	1.05, 1.15	<0.001
Role
Driver	1.05	1.02, 1.08	0.001
Passenger	1.23	1.18, 1.29	<0.001
Pedestrian/Other	0.99	0.93, 1.06	0.819
Region
Midwest	1.10	1.05, 1.16	<0.001
Northeast	1.16	1.09, 1.24	<0.001
South	1.07	1.03, 1.11	<0.001
West	1.08	1.03, 1.13	<0.001
Location
Rural	1.14	1.07, 1.21	<0.001
Urban	1.08	1.06, 1.11	<0.001

¹The statistical significance was defined as p<0.05. Statistically insignificant p-values are bolded.

²We regard p-value=0.05 as marginally statistical significance.

³The final year grouping (2011-2016) has 6 rather than 5 years.

^*OR, odds ratio; CI, confidence interval. The referent group is fatalities during control days.

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Editorial decision: Major revision
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Submission checks completed at journal
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You are reading this older preprint version

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Motor Vehicle Fatalities during Memorial Day Weekends, 1981-2016

Status:

Journal Publication

Version 1

Abstract

Figures

introduction

methods

Results

Figure 1. Odds Ratio and 95% CI for Motor Vehicle Fatalities during Memorial Day Weekends

discussion

limitations of the study

declarations

Ethics approval and consent to participate

No applicable.

Consent for publication

No applicable.

Availability of data and materials

The FARS dataset was derived from the Internet, at ftp://ftp.nhtsa.dot.gov/FARS and may also be accessed on the web at www-fars.nhtsa.dot.gov. The derived data are made available with the article.

Competing interests

The authors declare that they have no competing interests.

Funding

Author’s contributions

Acknowledgements

Not applicable.

references

tables

Status:

Journal Publication

Version 1