Can Driving Dehydrated Be As Dangerous As Driving Drunk?
Yes, driving dehydrated can be just as dangerous as driving drunk. A landmark study by Loughborough University and the European Hydration Institute found that mild dehydration causes driving errors to double creating a level of mental and physical impairment comparable to 0.08% Blood Alcohol Concentration (BAC)—the legal limit in the United States—or driving while sleep-deprived.
Dehydration is critical to healthy brain function to begin with, so this shouldn’t come as much of a surprise. Even mild dehydration can trigger headaches, fatigue, irritability, and impaired short-term memory and judgment — the same kinds of deficits that make drunk driving so dangerous.
Now that Michigan weather is getting hotter, it’s time to start thinking about drinking enough water — not just for your health, but also for your safety and the safety of other drivers on the road.
Driving dehydrated led to double the errors in landmark field study
The U.K. study consisted of two groups, each of which were told how much or how little to drink the day before the driving test. On the day of the test, each participant in the more hydrated group was given approximately 7 ounces of water once every hour, while the other group’s participants were given less than 1 ounce every hour (reaching mild dehydration status).
The two-hour driving test was split into four 30-minute sections. Both groups made more and more driving errors as the test progressed, such as drifting, car wheels crossing the rumble strip or lane line, and late braking.
The results showed a massive gap in safety:
- Total driving errors: The dehydrated group made 101 errors compared to just 47 errors in the hydrated group.
- Types of mistakes: Drivers experienced lane drifting, wheels crossing rumble strips, and late braking.
- Fatigue progression: Both groups made more mistakes over time, but the dehydrated group’s errors were consistently double.
The dehydrated drivers also rated worse for feelings of thirst, throat dryness, hunger, concentration and alertness.
Further, the report said that the dehydrated group’s performance was comparable to driving with a blood alcohol concentration of 0.08% — the U.S. legal driving limit — or while sleep-deprived.
As the study’s leader, Loughborough Professor Ron Maughan, noted:
“We all deplore [drunk] driving, but we don’t usually think about the effects of other things that affect our driving skills, and one of those is not drinking and dehydration. There is no question that driving while incapable through drink or drugs increases the risk of accidents, but our findings highlight an unrecognized danger and suggest that drivers should be encouraged to make sure they are properly hydrated.”
Why is driving dehydrated dangerous?
Driving dehydrated is dangerous because even mild fluid loss can impair the same cognitive and physical abilities alcohol does — slowing reaction times, clouding judgment, and reducing physical coordination. Since dehydration is often overlooked as a cause of driving impairment, it becomes a hidden danger that increases the risk of accidents without drivers even realizing they’re impaired.
The 4 dangers of driving dehydrated
Driving dehydrated directly impacts healthy brain function and physical coordination. Operating a vehicle without enough water impairs a driver in four distinct ways:
- Impaired judgment: Slower cognitive processing reduces focus, leading to poor decision-making and risky maneuvers.
- Delayed reaction times: Sluggish reflexes make it difficult to steer or brake quickly when unexpected road hazards appear.
- Reduced alertness: Dehydration causes sudden spikes in fatigue, irritability, and mood changes that distract from the road.
- Physical impairment: Mild to severe dehydration triggers headaches, dry mouth, muscle cramps, dizziness, and blurred vision.
How much water do I need to drink to stay hydrated
The National Academy of Medicine says that an adequate intake of total beverages a day is:
- Men: Approximately 13 cups of total beverages per day.
- Women: Approximately 9 cups of total beverages per day.
That sounds like a lot to ingest mentally and physically, but you need not just stick to water to reach that quota. Any kind of liquid-based drink, such as juice and milk and even soup, can keep you hydrated. Tea and coffee are OK, too — the caffeine amount does not discount the fluid in them as we always heard when growing up. Even though the caffeine produces a slight diuretic effect, it still counts as hydration according to the National Research Council’s Food and Nutrition Board.
6 ways to prevent driving dehydrated on the road
As the Michigan weather gets hotter, prioritize your hydration before you turn the key. Use these five practical habits to stay safe behind the wheel:
- Drink before you feel thirsty: Thirst means you’re already mildly dehydrated, so hydrate consistently throughout the day rather than waiting for your body to signal it needs water.
- Eat water-rich foods: Snack on high-water fruits and vegetables like cucumbers, watermelon, strawberries, and celery.
- Keep a bottle close: Place a spill-proof water bottle in your cup holder to sip frequently during the drive.
- Plan regular stops: Schedule rest breaks every two hours to rehydrate and stretch; never skip water just to avoid bathroom breaks.
- Monitor your body: Watch for warning signs like dry mouth, dark urine, or mild dizziness, and pull over to rehydrate immediately.
- Mind the AC and heater: Climate control systems dry out cabin air, which accelerates fluid loss through breathing during your drive.
Preventing driving dehydrated starts with prioritizing hydration
Preventing dehydration while driving starts with prioritizing hydration, just as you would check that your vehicle is safe and your seatbelt is fastened. Make it a habit to drink enough water, take breaks every two hours on long drives, and stay attentive to your body. If you feel thirsty or notice symptoms of dehydration, pull over safely and drink water. Staying properly hydrated helps maintain focus, reaction times, and alertness, keeping both you and other drivers on the road safer.
Injured in a car accident? Call the attorneys at Michigan Auto Law now for a free consultation!
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Written By
Steve M. Gursten,
Attorney,
License#: P53632
Steven Gursten, attorney at Michigan Auto Law and one of the most successful auto accident attorneys in Michigan. Michigan Auto Law represents people seriously injured in car, truck, motorcycle, and bus accidents, including catastrophic injury, traumatic brain injury, and No-Fault insurance cases. Steven has recovered the largest reported auto and truck accident settlement of any Michigan lawyer, and has been named Michigan Lawyer of the Year and a Top 50 Michigan Super Lawyer.
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