Permanent Daylight Savings Time

What can SAFTE-FAST add to the permanent Daylight Savings Time debate?

In March 2022, the United States Senate passed legislation, called the Sunshine Protection Act, to make daylight savings time (DST) permanent starting in November 2023(1). Sleep and circadian scientists were not happy about this. My favorite reaction to the passing of the bill came from the twitter account of a well-respected scientist returning home from a sleep conference in Europe: “A bunch of sleep and circadian scientists leave the US for a few days and what happens while we're gone? PERMANENT DST????” (Tweet available online at: /klknut).

Personally, I support the abolishment of DST for a single, non-scientific reason—drive-in movies can’t start until it’s dark out and I want to go to an outdoor movie that starts before 9PM! A colleague of mine countered with the argument that you need DST for late afternoon summertime golf games. Golf courses apparently are very interested in the debate about permanent DST, though some courses support Standard Time so that they can open earlier in the morning(2). Whether they support permanent DST or permanent Standard Time, most Americans agree that they no longer want to change their clocks twice a year(3). Right now, Americans are waiting to see how the U.S. House of Representatives votes on the Sunshine Protection Act, which has been held at the desk since March 16th, 2022.

The political debate on time change arrangements got me wondering, “what actual difference does a one-hour change in the timing of sunrise make?”. Proponents of permanent DST argue that more daylight in the evenings would increase economic activity, physical activity (ahem, golf!), reduce energy costs, and improve road safety. Opponents argue that yearlong DST may result in circadian misalignment and negative health effects as individuals will be forced to start their days before dawn during the winter months(4,5). Research results on the effects of DST on the economy, exercise, or energy costs have been mixed at best(6-13). The body of literature in support of permanent DST that I found most convincing was in the area of road safety. This argument suggests that permanent DST would improve road safety through a reduction of motor vehicle accidents related to darkness during evening commutes(14-17). The counterargument is that shifting light to the evening hours comes at the cost of light during early morning commutes(18). If only we had some way to examine potential differences in light exposure and fatigue risk during commute times in the year 2023 and beyond across a variety of U.S. locations, seasons, and work schedules. Then we could conduct an analysis on the effects of the time change arrangement alone, in the absence of any potential confounds like sleep deprivation or individual differences. Hmm. IF ONLY…. I think you can see where I’m going with this.

With some slight modifications, we used SAFTE-FAST with the AutoSleep function to predict sleep timing and sleep duration, Task Effectiveness, and light exposure in permanent DST conditions compared against permanent ST or current time conditions in day, evening, and night shift work schedules as well as school schedules and daily commutes in five major United States cities during autumn, winter, spring, and summer conditions for years 2023-2024. This analysis gave SAFTE-FAST a chance to flex some underappreciated muscles. SAFTE-FAST can predict Task Effectiveness during a commute buffer around work events and contains a NASA-provided algorithm for determining the available sunlight for any location on the globe for any date and time. SAFTE-FAST can use this light information to indicate the degree of concordance between the sleep-wake pattern and the rising and setting of the sun and to extrapolate information about light exposure during sleep, commute times, working hours, and across the entire day. This information is not a standard output in the software but is computed on the back end.

Our Operational Fatigue and Performance science group chose five cities across the U.S. as locations (New York City, Chicago, El Paso, Los Angeles, and Anchorage) and generated four different prospective work schedules—day shift (0900-1700), evening shift (1700-0100), night shift (2300-0700) and school schedules based on the average school start time per each city location’s state(19). We modeled fixed work schedules with 8-hour duration across the four seasons- autumn, winter, spring, and summer- and school schedules during autumn, winter, and spring. SAFTE-FAST modeled each day of the hypothetical schedules under assumptions of twice-yearly clock changes, permanent DST conditions, and permanent Standard time conditions. Output values of Task Effectiveness and light exposure were averaged across all days within each season. The scientific report of this analysis is currently under submission, but a preprint of the findings is available at A spreadsheet of the dataset is included with the preprint.

In the hypothetical work and school schedules we modeled, Task Effectiveness does not seem to be impacted greatly by permanent DST or Standard Time in comparison to current time arrangements. Permanent DST was associated with less light in the mornings, as we expected, but surprisingly, was associated with less light over the course of the waking day compared to Standard Time or the current system. Additionally, waketimes under permanent DST conditions would need to be before sunrise 63% of the modeled time compared to 42% under current conditions or 33% under permanent Standard time. This indicates that daylight is actually not getting saved by springing the clocks forward permanently.

The most surprising finding in this analysis came when we recategorized commute data by time of day to look at risk specific to morning rush hour (0700-0900) and evening rush hour (1600-1800). Task Effectiveness was lower during morning rush hour than evening rush hour because we included reverse commute data from the evening and night shift schedules. Shift workers are rarely discussed in the debate about DST. This data presents a new argument against DST for road safety—you would want to avoid darkness during rush hours when fatigued shift workers returning home have to share the road with students and daytime commuters (e.g., the morning). Now, this was a hypothetical computational analysis. Fixed evening and night shift schedules are not as common as rotating or changing schedules. Ironically, rotating schedules can exacerbate fatigue in shift workers as they scramble to readjust to a new routine. The modeled schedules also do not include professional drivers who may be fatigued on the road at any point of the day.

Daylight savings doesn’t seem to save much in a computational comparison averaged across a variety of U.S. cities, schedules, and seasons. Permanent Standard Time didn’t make much of a difference compared to the current system either, but the swap to permanent Standard Time may be less disruptive to work/school schedules as they currently stand. One thing that proponents of Permanent DST, opponents of Permanent DST, and biomathematical modelers of fatigue can agree on though, is that sleep and activity are tied to when you have to go to work. In that case, even if the House of Representatives passes the Sunshine Protection Act, employers who are worried about the impact of the time change on worker fatigue can always ask the team at SAFTE-FAST to identify schedule mitigation techniques to improve performance.


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19. Wheaton AGF, Gabrielle A; Croft, Janet B. School Start Times for Middle School and High School Students — United States, 2011–12 School Year. mm6430a1.htm?s_cid=mm6430a1_w. Accessed April 29, 2022.