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Collision-prone: When are you statistically most likely to get in an accident?

Collision data yields some surprising finds about the worst (and best) days to be on the road

  • Collision-prone

If you had to guess how many collisions are reported on average every day in Toronto, including the DVP and Gardiner (but not the 400-series highways), what would you say? Fifty? Seventy-five? One hundred? Try 158. Between Jan. 1, 2002 and Dec. 31, 2011, that adds up to nearly 579,000 collision incidents. And these are just the ones that are reported. compiled collision-report data for that 10-year period and found some interesting factors. (The data was obtained from the City of Toronto.) For example, which day of the week would you think is the most collision-prone? We found it’s Friday. As for the implications of bad weather, it’s pretty predictable: bad weather equals more collisions. But there’s one thing that seems to affect collision rates even more than snow: a change in temperature. Have a look at the charts below to discover these and other findings about when collisions happen and why, as well as the top five worst collision days ever.

First some good news about this 10-year data set: There were 25 per cent fewer collisions in 2011 than there were in 2002, some 54,000 compared to just over 72,000.

It’s not getting better:

The bad news is that 2002 and 2003 were high collision years and over the remaining eight years, the number of collisions has remained relatively constant, from a low of about 53,000 in 2006 to a high of nearly 56,300 in 2004. This suggests that road conditions and/or driver behaviour may not be improving.

Here’s the distribution by month:

The safest day on the road …

There were roughly 53,500 collisions in January over this period, compared with nearly 43,000 in April, the month with the fewest collisions. The fact that January is the worst month suggests that weather may be a major factor. Anybody who’s ever driven in a Canadian winter isn’t going to find that very surprising. But the fact that June is a worse month than either February, March or April tells you that weather is not the only factor. Sheer volume of traffic may also be a huge contributor; of the 10 days with the fewest number of collisions in this ten-year period, five are Christmas day. (Click here for the list of all days in the data range.)

Here are the days with 300 or more collisions.

What temperature has to do with it:

Although full data is not yet available for January 2012 on. But for the sake of comparison, Toronto Police Traffic services was able to confirm that on Jan. 6 of this year, a very bad day for drivers, there were 456 collisions reported. That would only rank as the eighth-worst day if added to our data period.

A story in the Toronto Star described the conditions on March 23, 2011. “The snow that fell … was wet snow that packed easily onto the roads.” … “Colder temperatures overnight may have also made road salt less effective.”

The amount of precipitation is one of the common factors in high-collision days. But the really bad days also tend to have a big drop in temperature, from above freezing to below. Between March 21 and 24, 2011, the temperature dropped 19 degrees from a high of 10C to a low of nearly -9C, with 636 collisions on March 23. Similar conditions were seen in January, 2003. Between the 8th and the 11th, the temperature dropped 13 degrees from a high of nearly 5C to a low of minus 8C. Add more than 7cm of snow on Jan. 9, and you have the third and fourth most collision-filled days, Jan. 9 (532) and 10 (504). A similar drop happens prior April 1, 2003, when there were 470 collisions. Here is a look at the months that contain the five most collision-filled days.

Worst day of the week? Friday:

Another factor shared by four of the five worst days is that they are weekdays. This fits the pattern of the most collision-filled days of the week, with Friday being by far the worst, followed by Wednesday, Thursday, Tuesday then Monday. Saturday (the second lowest) and Sunday (the lowest) tend to have far fewer than the weekdays.


But if weather conditions are severe, collisions can soar even on the weekend. The second most collision-filled day (549) was Nov. 16, 2002, a Saturday. The weather conditions were similar to the other top days, though it’s possible that having conditions like these so early in the season caught so many drivers off guard that the effect was disproportionately severe. It’s also possible that many drivers had no put their winter tires on by mid-November.

In the Star story about the worst day, Toronto Police said they were expecting the huge number of collisions to continue the following day. But that didn’t happen. In fact, collision numbers tend to spike for one day and then fall way off (with the exception of Jan. 9-10, above). One possible reason is that salting and snow clearing by the city tends to be quite effective. It’s also possible that drivers are more cautious in the days following a particularly treacherous drive.

But the collision data offers some lessons for drivers. The next time we get a dump of snow and/or rain, coupled with a big drop in temperatures from plus to minus, especially on a weekday, avoid driving if you can, or take it easy if you can’t. And if this seems obvious, tell that to the 636 drivers who were stuck at the collision reporting centres on March 23, 2011.



By Aneurin Bosley for an editor at

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