The House passed the Sunshine Protection Act this month, which would make daylight saving time permanent and end the twice-a-year clock change. Most sleep and circadian scientists rank permanent DST as the worst of the three options, because it moves winter's limited daylight from the morning (when the body clock uses it to stay synchronized) to the evening (when commerce prefers it). The strongest caveat comes from a 2026 review of 157 studies, which found the evidence for uniform harm thinner than the advocacy implies. Source: NYT, Jul 27 2026 — Lynne Peeples.

Congress is choosing among permanent daylight saving time, permanent standard time, and the seasonal switching we have now. The total daylight is fixed by latitude and season. The only lever is placement of the clock hour.

Permanent DST buys brighter evenings at the cost of dark mornings. In Seattle it would push winter sunrise past 8:30 a.m. for about ten weeks, sending high-schoolers to first period in the dark. Permanent standard time does the reverse, delivering pre-4:30 a.m. summer sunrises. The country ran the permanent-DST experiment once, in January 1974 during the oil crisis. Support collapsed within months after children were struck walking to school in the dark, and Congress reversed it.

The transition harms are the most consistent finding. Registry data show the spring "spring-forward" raises the risk of fatal traffic crashes by about 6 percent, concentrated in the morning and toward the western edge of each time zone, where the sun already rises late by the clock (Fritz, Current Biology 2020). The same transition tracks with short-term upticks in heart attacks and measurably worse sleep, with evening chronotypes hit hardest (Romigi, Sleep Medicine Reviews 2025). The fall "fall-back" shows no comparable crash signal, which points to sleep loss and misalignment rather than the clock ritual itself.

The case for permanent DST rests mostly on where people are awake to use the light. One analysis estimated that year-round DST could prevent roughly 171 pedestrian and 195 vehicle-occupant deaths a year, because evenings carry more traffic than mornings (Coate & Markowitz, Accident Analysis & Prevention 2004). Extra evening light also tracks with lower robbery rates.

Almost every claim about a permanent regime is an extrapolation. The data come from clock transitions, short DST extensions, or "natural experiments" comparing people at opposite edges of a time zone. Living on the late-sunrise western edge correlates with less sleep, lower wages, and higher rates of some cancers and suicide — a proxy for permanent DST, not a test of it. A dedicated road-safety systematic review concluded the evidence can neither support nor refute a permanent morning-to-evening light shift.

The largest synthesis to date, a pre-registered review of 157 studies across 36 countries, reached a deliberately unsatisfying verdict: the effects of clock changes and summer DST are "not uniformly detrimental," and the honest move is to mitigate the known harms while better evidence accrues (Steponenaite & Lewis, European Journal of Epidemiology 2026). Modern life muddies the biology further. People spend days under dim indoor light and evenings under bright artificial light, which flattens the day-night contrast the whole circadian argument depends on.