Chart 1. The chart above shows the hourly activity of aggregated reported crashes in Illinois in 2010. It shows the hour of the day, that, throughout the year, saw the most injuries and fatalities.
The League of Illinois Bicyclists (LIB) recently posted a link on its Facebook page to an event in August called “Designing for Bicycle Safety”, hosted by the Chicago Metropolitan Agency for Planning (CMAP). A person commented,
We can design for bike safety until we are blue in the face, but unless bicyclists come to their senses and buy lights and reflective clothing for riding after dark – there will continue to be needless rider deaths and incapacitating injuries. I believe this needs to be top priority in rider awareness education.
Safer infrastructure should be the top priority in all things bicycling, and when it comes to reducing crashes at night, we agree that encouraging cyclists to use lights at night is important (Get Lit!). I wanted to know just how many crashes occur at each hour of the day. As is usual when it comes to bike crash data crunching, it takes longer than I originally thought or planned to get the full answer. In essence, though, the majority of crashes and injuries occur during “evening rush hour” while the majority of fatalities, while very small, occurred at night.
Update July 27, 2012: New, interactive charts show the same data in different ways.
Notes about this data
The majority of people involved in crashes in Illinois were in Chicago. I ran the numbers for the entire state of Illinois as this in response to a comment on the League of Illinois Bicyclists’s Facebook page. The data only applies to the year 2010, as that is the only year for which I have statewide crash data. The data only includes crashes reported to the police. The frequency of unreported crashes is unknown; hospital records would need to be consulted to gain a better understanding of how many crashes were not reported.
Data and interpretations
- The most crash-frequent hour for fatal bike crashes was 8-8:59 PM.
- The most crash-frequent hour for anyone receiving an injury (regardless of severity, but disregarding fatal crashes) was 5-5:59 PM.
- The most crash-frequent hour for anyone receiving an incapacitating injury was 6-6:59 PM.
- The most crash-frequent hour for anyone receiving an incapacitating injury, or who died in the crash, was the same, 6-6:59 PM.
The hour with the most crashes that resulted in fatalities was 8 PM to 8:59 PM, with 5 fatalities in Illinois in 2010. There was one in April, two in July, and one each in August and September. If you look at fatalities in two hour time blocks, you get the following, selected, results (each number in this article represents a person, not a crash):
- 7-8:59 AM: 2
- 9-10:59 AM: 3
- 11 AM-12:59 PM: 0
- 1-2:59 PM: 1
- 3-4:59 PM: 2
- 5-6:59 PM: 3
- 7-8:59 PM: 6
- 9-10:59 PM: 3
Only 3.9% of people in reported bicycle crashes in Illinois in 2010 walked away with no injury.
I’ll have to run a separate analysis to match up these times with the months in which they occur, so there’s a better understanding of which occurred before sunset and which occurred after, but generally, the crash rate follows ridership, and ridership follows the seasons.
Hourly ridership data is still lacking in Chicago; the Department of Transportation does monthly counts in the same locations but only for 4 hours each time (7-9 AM and 4-6 PM), one day per month (here’s July’s data). Automated bike count devices, like the EcoTotem from Eco-Counter, should be installed around the city to collect constant and consistent data every day of the year. With that information we can better understand the seriousness of the hourly crash rates and find anomalies in the data (for example, if the majority of crashes were occurring in the 5-5:59 PM period but the majority of cycling in the evening was from 6-6:59 PM – the information isn’t there).
Chart 2. This chart shows the monthly proportions of injury outcomes in reported bike crashes in Illinois in 2010. The outcomes appear relatively the same, except for a decrease in injuries in January and February. March and December have the lowest “no injury” proportions.
We could also find out if more people are crashing or being injured than expected. For example, are there more crashes and injuries at night on a weekend, or on a weekday? Why do injuries peak on Wednesday? What’s different about cycling ridership on Wednesday than Tuesday or Thursday?
Chart 3. This chart shows injury activity of aggregated reported crashes in Illinois in 2010 by day of the week. Wednesday is the day of the week that sees the most injuries with Friday seeing the second most.
A reader commented on the photo when it was posted earlier suggesting that crash rates on Friday and Saturday nights would be “sky high”. Here is the weekend breakdown:
- Thursday night, 10 PM to 4 AM: 28 injuries, 1 fatality
- Friday night: 10 PM to 4 AM: 55 injuries, 0 fatalities
- Saturday night: 10 PM to 4 AM: 53 injuries, 1 fatality
- Sunday night: 10 PM to 4 AM: 31 injuries, 0 fatalities
How does knowing when crashes occur help advocates hone their strategies in reducing the number of injuries, a goal in the Bike 2015 Plan?