Data analysis: road fatalities part 2 – by date

By Joel Johnson

Although the road toll for a particular day of the year is somewhat stochastic, it would be expected that some days have a higher fatality rate, and some days have a lower rate. Factors such as school holidays play a large role. This investigation seeks to determine the most dangerous and safest days of the year, using road fatality data provided by the Bureau of Infrastructure, Transport and Regional Economics (1).

METHOD
The dataset consists of 46,075 fatalities between 1989 and 2015 (1). The number of fatalities on each day of the year was analysed using Excel software, in order to determine any patterns that might be present. There were 6 leap years in a total of 26 years between 1989 and 2015; therefore there was an average of 0.2308 extra days over this period. This also meant that the day 29 February occurred 0.2308 times as often as all the other dates, so the number of deaths for the 29th of February was adjusted by multiplying it by 4.3333 (1/0.2308).

RESULTS
The theoretical average number of deaths that should occur on any one day was calculated to be 126.15 (46075 deaths / 365.2308 days per year). The graph below shows the data arranged by day. In total, there were 183 days that had an above average number of deaths, and 183 days below average.

Fatalities by date.png

There was a small amount of fluctuation between different among months (up to 6.8%), with December, then March being the most dangerous months. The safest month was July, followed by January.

Fatalities by month.png

The most dangerous day of the year was the 22nd of December, on which 171 deaths occurred (35.6% above average). This is not unexpected, as it is 3 days before Christmas, and there are many families travelling at that time. The 23rd December was also significantly above average, with 157 deaths, supporting this hypothesis.

On the other hand, the safest day of the year was the 15th of January, which had only 86 deaths (31.8% below average). This date is somewhat unusual, as it is still in the school holidays; however it is likely that most people would have stopped travelling by this time.

Table 1 – Eleven Most Dangerous Days

Day Number of Deaths (1989-2015)
22 December 171
20 December 166
18 February 166
9 December 165
13 August 163
21 November 161
25 September 159
22 January 158
23 December 157
16 November 155
25 March 155

The 29th February had only 31 deaths, however this equates to 134 deaths (6.5% above average) when adjusted for the fact that it only occurred in 6 of the years.

For cyclists, the most dangerous day was the 28th February, with 13 deaths (377% above the average of 3.45). The safest days were the 14th January, 3rd February, 5th March, 14th, 15th July and 24th July, and the 24th August, all of which had no deaths recorded.
For pedestrians the worst day was the 12th April (38 deaths; 196% above the average of 19.37) and the safest day was the 10th January (5 deaths; 74.2% below average).

This information could be used by the Department of Transport and Main Roads (DTMR) for selective ‘nudging’ of behaviour. Although the DTMR does broadcast road safety reminders during peak road fatality times such as school holidays, the frequency of such advertisements could be increased on the peak days (e.g. 20th, 22nd and 23rd December).

CONCLUSION
Although the number of road deaths on a particular date is relatively random, there are noticeable patterns that can be explained by the expected incidence of road use.

REFERENCES
1. Department of Infrastructure and Regional Development 2016, Australian road deaths database: fatalities, Australian Government. Available from: https://bitre.gov.au/statistics/safety/fatal_road_crash_database.aspx.
[7 April 2016].

 

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