Memorial Day Traffic Fatality Estimate

A frequently asked question is “How much more dangerous is travel over the Memorial 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 Memorial Day weekend. This chart shows the fatality data from FARS for 1995 to 2017 for comparable weekends. The average number of traffic deaths during Memorial Day over the last six years is 6.3% higher than the average number of traffic deaths during the comparison periods (358 vs. 336 deaths). The difference between these two means is not statistically significant at the .05 level.

  • Chart
  • Data Table

Source: NSC analysis of NHTSA FARS data

NSC also compares the Memorial Day holiday to other holiday periods. When comparing holiday periods of different lengths, an average fatality per day rate is used. The Memorial Day holiday, along with the other summer time holidays (Independence Day and Labor 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.

  • Chart
  • Data Table

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 6.3%, then the risk of dying in a traffic crash during the Memorial Day holiday period is less than during comparable non-holiday periods. If the travel increase is less than 6.3% 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 Memorial 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 are 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 May 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 Memorial 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 May and traffic fatalities from crashes that occurred during the holiday period. From 2012 to 2017, fatalities from crashes during the Memorial Day holiday period averaged 11.04% of the total fatalities in May.

Traffic deaths during the Memorial Day period as a percent of total motor-vehicle deaths in May

Year May Memorial Day Period Percent
2012 3,190 367 11.50%
2013 2,980 334 11.21%
2014 3,038 337 11.09%
2015 3,339 370 11.08%
2016 3,481 392 11.26%
2017 3,416 345 10.10%
6-year average 3,241 358 11.04%

Source: NCHS and NHTSA FARS data

 

A time series model was developed to forecast an estimate of total traffic deaths for May 2019. An Autoregressive Integrated Moving Average model was constructed based on 48 months of traffic deaths recorded from April 2015 through March 2019. This model was chosen because of the seasonal pattern in traffic deaths. The model was developed using the SPSS/PC+ Version 22.0 statistical computer package. The model forecasts total traffic fatalities for May 2019 to be 3,440. Multiplying the projected total fatalities by the fraction obtained in the first step gives an estimate of 380 traffic fatalities from crashes during the holiday period.

The 90% confidence interval for the estimate of total May motor-vehicle deaths is 3,221 to 3,674. If we assume the fraction of May deaths that occur during the Memorial Day period is normally distributed, then the 90% confidence interval for that fraction is 10.64% to 11.44%. Combining these two estimates gives the confidence interval for the Memorial Day period estimate: 343 to 420 traffic deaths.