Lauren Domnick's picture

Mar 15, 2017


Lauren Domnick

Director of Analytics & Modeling

If you or your drivers are feeling a little sluggish behind the wheel this week, blame Ben Franklin.

His essay in a French newspaper suggesting that citizens of Paris shift their clocks by one hour in order to reduce their spending on candles is having some unintended negative consequences for truck drivers in America 233 years later.

While Daylight Saving Time does give us longer daylight hours at the end of the day, it also takes some getting used to. And that manifests itself for truck drivers, at least it seems, in a more than modest uptick in accidents.

We looked at commercial truck-involved accident data from a six-week period before and after shift to Daylight Saving Time a year ago and did see a 17 percent spike in the number of accidents in the week following the time change compared to the week before. Specifically, there were 648 reported accidents in the week of March 13 through March 19 last year (the time change took effect early on March 13). The previous week there were 555 reported crashes involving commercial trucks.

The second week after the time change saw a drop back to 590 reported crashes, followed by 561 and 524 in the two subsequent weeks, respectively. 

Time change impairs more than commercial drivers

Is that definitive proof that the switch to Daylight Saving Time triggers something between a 10 percent and 20 percent increase in the probability of truck crashes in the following week? No. We don’t know what the weather conditions were like and what other changes were happening during those weeks. Nor are we fully informed on some of the other factors that could have impacted driver performances.

But this data snapshot, like others done by different organizations from time to time over the years, does imply, perhaps strongly, that the Spring time change triggers a short-term decline in highway safety performance. 

Those who’ve looked at this phenomenon in hopes of determining why it seems to happen have focused on four likely causes:

  • Sleep pattern disruption. The human circadian rhythm — the normal cycle of sleeping, eating, working, relaxing, and sleeping again — is sensitive both to time zone changes and to changes in light and dark cycles. Disrupted sleeping and eating patterns typically lead to feeling sluggish, especially in the mornings. Reaction times are slowed because of the combination of reduced mental acuity and diminished physical response times. It can take jet lagged air travelers up to a week to fully acclimate to a new time zone. For drivers, the time zone changes aren’t as significant, but even a one-hour change can have a noticeable impact on human performance. 
  • Longer “awake periods.”  Many drivers find it hard to sleep while the sun is up, so they drive later into the evenings. But many then fail to compensate and wake up at their regularly scheduled time, meaning that on a net basis they get less rest and time in the bunk. Tougher driver duty time laws help to counter that problem. But just because a driver isn’t driving doesn’t mean he or she is asleep. Longer rest breaks during the day do not fully offset a missed hour or two of sleep at night. 
  • Traffic pattern changes. While Daylight Saving Time gives drivers better light conditions for driving in the evening, it also means many drivers hit the road in the morning an hour or more before sunrise. Thus, for many drivers that will mean driving through the morning rush in the dark (at least for another month or so, and then again in October). 
  • Non-professional drivers are more sensitive to Time Change-related physical and situational disruptions than commercial drivers and, arguably, more likely drive sloppily or groggily. Our March 2016 accident tracking data does not tell us anything about the cause of all those additional accidents in the week or two after the Spring Time Change. But that temporary degradation in ordinary drivers’ skills represents an increased challenge and threat to professional drivers. 

Frankly, there’s not enough solid research on the subject to draw definitive conclusions about the impact of the spring time change on highway safety. But even if the anecdotal evidence and common assumptions about that are proven wrong, the jump to Daylight Saving Time still serves as a great reminder to drivers and the whole trucking industry.

Everyone needs to be fully-engaged and alert on the roads at all times. And that’s especially true after we make the jump to Daylight Saving Time.

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