A frequently asked question is “How much more dangerous is travel over the Labor Day holiday?” Two aspects of this question must be considered: “Compared to what?” and, “What about changes in the amount of driving?”

NSC compares the holiday to periods of similar length, specifically from 6 p.m. Friday to 11:59 p.m. Monday, during the weeks immediately before and after the Labor Day weekend. This chart shows the fatality data from FARS for 1996 to 2016 for comparable weekends. The average number of traffic deaths during Labor Day over the last six years is 10.5% higher than the average number of traffic deaths during the comparison periods (376 vs. 340 deaths). The difference between these two means is statistically significant at the .05 level.

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Source: NSC analysis of NHTSA FARS data

NSC also compares the Labor Day holiday to other holiday periods. When comparing holiday periods of different lengths, an average fatality per day rate is used. The Labor Day holiday, along with the other summer time holidays (
Memorial Day and Independence Day) have the highest average fatality rates per day. Thanksgiving, Christmas and New Year’s Day holidays tend to have lower average fatality rates per day.

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Source: NSC analysis of NHTSA FARS data

The second question concerns changes in the amount of travel or exposure. NSC is not aware of any data system that tracks changes in vehicle miles of travel by day of the year on a national basis. Lacking an objective measure of exposure change, NSC assumes travel is greater on holiday weekends than on non-holiday weekends.

If the assumed travel increase exceeds 10.5%, then the risk of dying in a traffic crash during the Labor Day holiday period is less than during comparable non-holiday periods. If the travel increase is less than 10.5% or if travel is actually lower, then the risk of dying on the holiday is greater than during comparable periods.

Estimate methods

The objective is to estimate the number of deaths that will occur in traffic crashes during the Labor Day holiday period based on data available several weeks before the holiday. The estimate developed by NSC includes all traffic deaths from crashes during the holiday period.

The general procedure involves three steps. First, historical data is used to determine the average fraction that holiday fatalities are of the total motor vehicle deaths for the month. Second, total traffic deaths for the coming month in which the holiday falls are estimated using a time series forecasting model. Third, the projected total for the month is multiplied by the fraction to obtain the holiday estimate.

Holiday as percent of monthly fatalities: Total September motor vehicle deaths are calculated using the latest six years of final data available from the National Center for Health Statistics. Traffic fatality estimates for the Labor Day period are calculated using data from the National Highway Traffic Safety Administration Fatality Analysis Reporting System.

The table shows total motor vehicle fatalities for September and traffic fatalities from crashes that occurred during the holiday period. From 2011 to 2016, fatalities from crashes during the Labor Day holiday period averaged 11.79% of the total fatalities in September.

Traffic deaths during the Labor Day period as a percent of total motor-vehicle deaths in September

Year September Labor Day Period Percent
2011 2,930 373 12.73%
2012 3,070 378 12.31%
2013 3,170 371 11.70%
2014 3,069 362 11.80%
2015 3,372 394 11.68%
2016 3,612 379 10.49%
6-year average 3,204 376 11.79%

Source: NCHS and NHTSA FARS data

A time series model was developed to forecast an estimate of total traffic deaths for September 2018. An Autoregressive Integrated Moving Average model
 was constructed based on 48 months of traffic deaths recorded from July 2014 through June 2018. This model was chosen because of the seasonal pattern in traffic deaths. The model was developed using the SPSS/PC+ Version 5.0 statistical computer package. The model forecasts total traffic fatalities for September 2018 to be 3,560. Multiplying the projected total fatalities by the fraction obtained in the first step gives an estimate of 420 traffic fatalities from crashes during the holiday period.

The 90% confidence interval for the estimate of total September motor vehicle deaths is 3,272 to 3,873. If we assume the fraction of September deaths that occur during the Labor Day period is normally distributed, then the 90% confidence interval for that fraction is 11.16% to 12.41%. Combining these two estimates gives the confidence interval for the Labor Day period estimate: 365 to 481 traffic deaths.