Fatal Traffic Risks With a Total Solar Eclipse in the US

Abstract

This case-control study describes the incidence of fatal traffic crashes in the US during the 2017 total solar eclipse.

A total solar eclipse occurs when the moon temporarily obscures the sun and casts a dark shadow across the earth. This astronomical spectacle has been described for more than 3 millennia and can be predicted with high precision. Eclipse-related solar retinopathy (vision loss from staring at the sun) is an established medical complication; however, other medical outcomes have received little attention.¹

The 2017 total solar eclipse was widely anticipated because the path of totality (locations experiencing a total eclipse) fell within 300 miles of driving distance for a third of all individuals in the US. An estimated 20 million people in the US traveled away from home to another city to view the eclipse, resulting in substantial road traffic.² We hypothesized that the eclipse was associated with increased risks of a fatal traffic crash.

Methods

For this matched case-control study, we obtained data from the National Highway Traffic Safety Administration Fatality Analysis Reporting System, a registry of all fatal traffic crashes on public roads in the US. We focused on the 3-day exposure interval centered on the day of the eclipse (August 21, 2017), reasoning that a substantial amount of eclipse-related travel occurred on adjacent days. To account for seasonal and weekly variations in risk, we selected 3-day control intervals a week before and a week after the eclipse (August 13, 14, and 15, and August 27, 28, and 29), matching by day of week.³ The study protocol was approved by the research ethics board of Sunnybrook Health Sciences Center, including a waiver of direct patient consent. This study followed the STROBE reporting guideline.

We used an official US Navy calculator to categorize crash timing relative to the time of maximal eclipse based on crash-specific location latitude and longitude.⁴ The primary analysis used negative binomial regression with adjustment for day of the week to compare the number of individuals in fatal crashes during the 3-day eclipse exposure interval with the number during the matched control intervals. Statistical significance was based on P values <.05, using 2-tailed tests.

Results

A total of 741 individuals were involved in fatal crashes over the 3-day eclipse exposure interval (10.3 per hour) and 1137 individuals were involved in fatal crashes over the 6 control days (7.9 per hour), corresponding to a significant increase in traffic risks around the time of the eclipse (relative risk, 1.31; 95% CI, 1.15-1.49; P < .001). In absolute terms, this averaged to 1 extra crash-involved person every 25 minutes and 1 extra crash fatality every 95 minutes.

Relative risks were consistent among diverse subgroups and accentuated under clear weather conditions (Figure 1). Observed crash risks varied over time (Figure 2). Secondary sensitivity analyses yielded similar results. The overall relative risks were similar in magnitude to the increased traffic risks observed around Thanksgiving, Memorial Day, or the July 4th weekend.⁵

Figure 1. Relative Risks for Different Subgroups.

Vertical axis indicates neutral risks; solid squares, estimates; and horizontal lines, 95% CIs. Relative risks compare eclipse with control intervals (logarithmic scale). Primary analysis for the full cohort is presented at the bottom. Results show increased relative risk associated with eclipse extending to diverse subgroups. In Canada, the term racialized indicates that race is a societal vs biological categorization and is often used to describe individuals of races other than White.

Figure 2. Fatality Risks at Different Times.

Time 0 indicates the eclipse moment (according to local time). Results show the orange area exceeding the blue area, suggesting higher risks associated with the eclipse.

Discussion

During the 2017 total solar eclipse, the path of totality was narrow (about 70 miles wide) and the eclipse lasted less than 3 minutes in any one place (maximum duration of 160 seconds in Carbondale, Illinois). The increased traffic risks are difficult to attribute solely to transient changes in ambient light. Instead, the findings likely derive from increases in traffic. Other potential factors include travel on unfamiliar routes, speeding to arrive on time, driver distraction by a rare celestial event, drug- or alcohol-induced impairment from eclipse-related celebrations, and eclipse viewing from unsafe roadside locations.

The next total solar eclipse will occur on April 8, 2024, and is within driving range for more than 200 million individuals within the US. To help prevent another possible surge in traffic fatalities, clinicians might advise patients to respect speed limits, minimize distractions, allow greater headway, wear a seatbelt, and avoid driving while impaired. More broadly, stakeholders should work toward a transportation system that minimizes crash risks, tolerates human error, and optimizes recovery after a crash.⁶ These population-based interventions may prevent eclipse-related fatalities and potentially save lives throughout the year.

Supplement.

Data Sharing Statement