Driving with any lights on during day safer than without

Q: Both our cars have running lights that come on automatically, but because they aren’t as bright as headlights and don’t turn on rear lights, we tend to drive after manually turning on headlights during daylight hours. Is this any safer?

A: I can’t find any research comparing the safety of headlights and daytime running lights (DRLs.) But there are plenty of studies showing that some light is better than none. Driving with your DRLs or headlights on during the day reduces your risk of a crash in every country except the United States. The study by the National Highway Traffic Safety Administration was “not statistically significant.” However, several states did their own studies and reached similar conclusions: vehicle lighting reduces crashes, especially collisions with pedestrians and motorcycles, two of the highest-risk road user groups.

Starting with Scandinavian countries in the 1970s, many countries now require cars to be equipped with DRLs. It makes sense that the first countries to adopt DRLs were ones with a lot of gray winter days (kind of like Western Washington.) In the US they’re not required, but available on many vehicles.

Early complaints about DRLs included increased fuel consumption and bulbs that burned out more often. It does take some energy to illuminate the lights on your vehicle, and that power comes from the gas in the tank. With modern LED headlights, those problems aren’t really an issue. Low-beam LED headlights consume as little as 15 watts, and DRLs are down around five watts. If that means nothing to you, how about this: If you drove 100,000 miles with your headlights on, you’d consume one extra gallon of gas. With DRLs, it would take about 300,000 miles to use up an extra gallon of gas. That’s farther than most cars last. And you might go over two million miles before the lights burn out.

The one remaining problem with DRLs is that the system doesn’t light up any bulbs on the rear of the vehicle (at least with most cars.) As long as drivers remember to turn on their headlights before it gets dark, it’s not too bad. But with those DRLs lit up it might seem like the headlights are already on, especially in an environment with lots of street lighting. I’d bet that the risk of getting rear-ended at night offsets the benefit of increased visibility during the day.

Actually, there’s another problem. DRLs aren’t meant to help you see; they’re intended to help other drivers and pedestrians see you. Their lower power makes them poor headlights once it gets dark, and drivers who think their headlights are on won’t be seeing as much as they should.

With DRLs, carmakers have built a feature that doesn’t account for human failure. No matter how hard we try, humans are never going to be perfect, and sometimes that includes thinking your DRLs are your headlights. There is an alternative, as suggested in the original question. Turn on your headlights when you start your car. Even easier, if you have a car equipped with automatic headlights: select the automatic position and your headlights will come on any time they’re needed.

Good lighting won’t fix bad driving, but for the attentive driver, keeping your lights on during the day can reduce your risk of a crash by somewhere around 10%.

Doug Dahl writes a weekly column for this newspaper. He is with the state Traffic Safety Commission.