Safest day to cycle?

Here’s a count of all cycling fatalities in California from 2001 to 2012, tabulated by year and day of week. The raw data comes from SWITRS.

	Monday	Tuesday	Wednesday	Thursday	Friday	Saturday	Sunday
2001	10	17	18	21	20	21	14
2002	16	16	15	19	26	15	13
2003	19	19	15	20	19	18	15
2004	17	11	13	20	12	17	34
2005	16	21	16	18	18	20	23
2006	17	20	22	23	28	22	23
2007	14	21	23	17	15	21	14
2008	16	19	23	16	20	11	26
2009	18	13	18	7	22	15	16
2010	22	8	10	19	18	14	20
2011	21	14	23	15	22	29	18
2012	21	16	23	26	28	22	16
Totals	207	195	219	221	248	225	232

Is there any knowledge to be gleaned here about the safest day to cycle? One of the biggest problems in analyzing SWITRS cycling data comes from the lack of base rates, or overall counts of cyclists for a given period. The single worst day came from the 34 people who died on Sundays in 2004, but without knowing whether many people were cycling on Sundays in 2004, we can’t determine the rate of fatalities, and there’s not much we can derive about safety from these numbers. In a word, then, we don’t know when it’s safest to ride.

Still, my guess is that cycling rates climb on the weekends. If that’s true, we should expect to see higher fatalities overall on Saturdays and Sundays. They don’t show here in the totals for the weekends, which look rather like the rest of the week. The cause could be as simple as less car traffic on the weekends, or as rich and complex as this notion of safety in numbers, the idea that so many people are cycling on the weekends that drivers notice them.

Ultimately, we really need better information about cycling in California. We don’t know much about ourselves, how many of us ride, when we do, how we get into crashes, and why.