Twice a year, when the clocks shift by an hour, British drivers face a jarring mismatch: the routes they know by heart are suddenly flooded with low sun or plunged into early darkness. And twice a year, crash numbers climb. A 2020 study in Current Biology found that the spring clock change alone was associated with a 6% increase in fatal traffic collisions in the United States during the week that followed, driven largely by disrupted sleep and altered light conditions. While UK-specific figures are harder to isolate, road safety charity RoSPA has long warned that the weeks after each clock change are among the most dangerous on British roads.
Against that backdrop, safety organisations are pushing a deceptively simple message ahead of the March 2026 spring change: keep a proper pair of driving sunglasses in your car at all times.
Why the clock change catches drivers out
When clocks spring forward at 1am on the last Sunday of March, most people lose an hour of sleep. Research from the American Academy of Sleep Medicine suggests it takes the average person two to three days to fully recalibrate their circadian rhythm after the shift. During that window, reaction times slow, concentration dips, and the kind of split-second hazard perception that prevents collisions is measurably impaired.
At the same time, the angle of the sun changes relative to commuters’ usual schedules. A driver who spent all winter with the sun safely below the roofline on the school run may suddenly find it sitting squarely at eye level. RoSPA’s seasonal guidance notes that low sun is a contributing factor in a significant number of collisions each spring and autumn, particularly on east-west routes during the morning and late afternoon peaks.
The combination is potent: a tired driver, on a familiar road, facing light conditions their brain has not yet adjusted to.
The hidden danger of low sun and glare
Low sun does not just cause discomfort. When it strikes a wet windscreen or reflects off damp tarmac, it can create a near-total whiteout that lasts several seconds. In that time, brake lights, pedestrians on crossings, and cyclists can vanish from view entirely. The RAC has noted that glare effectively extends stopping distances because drivers either hesitate or simply cannot see a hazard until they are far closer than they would be under normal conditions.
Dirty or smeared windscreens make the problem dramatically worse. Light scatters across micro-scratches and road film, turning a manageable glare into an opaque haze. Keeping the inside and outside of the windscreen clean, topping up screenwash, and replacing worn wiper blades are all standard advice from motoring organisations ahead of each clock change. But even a spotless windscreen cannot fully compensate when the sun is directly in a driver’s eyes.
That is where eyewear comes in.
Why one pair of sunglasses makes such a difference
The advice from road safety bodies is not to grab whatever pair is lying around the house. It is to keep a dedicated, suitable pair of sunglasses permanently in the car, ideally in the glovebox or a door pocket where they can be reached without fumbling. The logic is straightforward: glare strikes without warning, often mid-journey, and a driver who has to squint through it for even 30 seconds is a driver whose hazard perception has collapsed.
Motoring safety specialists have stressed that the sunglasses must be appropriate for driving. Fashion pairs with extremely dark lenses, typically rated as Category 4 under the British and European standard BS EN ISO 12312-1, are designed for high-altitude or desert conditions and are explicitly not recommended for driving. They restrict too much light, making it difficult for the eyes to adjust when moving from bright sun into shade, a tunnel, or under a bridge.
What kind of sunglasses are safest for driving
The College of Optometrists and several UK motoring organisations recommend Category 2 or Category 3 lenses for driving. Category 2 lenses allow 18% to 43% of light through and suit overcast-but-bright conditions. Category 3 lenses allow 8% to 18% through and are better for strong, direct sunlight. Both categories preserve enough visibility for a driver to read road signs, spot pedestrians in shadow, and react to brake lights without delay.
Lens colour matters too. Grey and brown tints are generally preferred because they maintain natural colour perception, which means red brake lights and amber signals look the way the brain expects them to. Green tints can also work well. Blue, yellow, or rose-tinted lenses may distort colour in ways that slow recognition of traffic signals or emergency vehicles.
Polarised lenses are worth considering. They are particularly effective at cutting horizontal glare from wet roads, puddles, and the roofs of other vehicles. However, drivers of cars with head-up displays or certain LCD instrument clusters should test polarised lenses with their own vehicle first, as polarisation can sometimes make digital readouts appear dim or patchy at certain angles.
For drivers who wear prescription glasses, prescription driving sunglasses or clip-on polarised filters are practical alternatives. Leaving a pair in the car removes the temptation to drive without them on a bright morning simply because they were forgotten at home.
How glare, fatigue, and behaviour combine after the switch
Sunglasses address glare, but the post-clock-change risk is a package. Sleep disruption, altered light, and shifted traffic patterns all feed into each other. A 2020 analysis published in Current Biology by researchers at the University of Colorado Boulder found that the spring transition was consistently linked to higher fatal crash rates, with the effect most pronounced in the mornings and in locations further west within their time zones, where the sun rises later relative to clock time.
In the UK, RoSPA’s guidance on the clock change highlights that pedestrians and cyclists are disproportionately affected because they become harder to see in transitional light. Drivers who are already fatigued from a disrupted night’s sleep are less likely to scan effectively for vulnerable road users, particularly at junctions and crossings where low sun may be directly behind a person on foot.
Practical steps beyond sunglasses include adjusting sleep schedules by 15 to 20 minutes in the days before the change, leaving extra following distance during the first week, and being especially cautious on routes with east-west orientation during peak commute times. Some fleet operators and driving instructors also recommend using the sun visor in combination with sunglasses for the worst angles, rather than relying on either alone.
None of this is complicated or expensive. A pair of Category 2 or 3 driving sunglasses can cost as little as £10 to £15 from a reputable retailer. Stored in the car, cleaned occasionally, and actually worn when the sun is low, they address one of the most common and most preventable causes of impaired visibility on UK roads. With the clocks set to spring forward in late March 2026, now is the time to check the glovebox.
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