Road Rules: Turns signals in emergency situations, headlights in the daytime


Recently, someone asked Doug Dahl, Target Zero manager for the Washington Traffic Safety Commission, a question about needing to use an emergency signal while performing an emergency maneuver on the road.

“If I must avoid a head-on collision requiring a spontaneous and immediate response, am I breaking the law if I do not use a turn signal at this moment,” the question further asked.

Dahl’s answer:

“Right now a bunch of BMW drivers are confused by this question. They’re asking themselves: “How can turn signals possibly be required in an emergency? I didn’t think they were even required for ordinary driving.”

“The great driving instructor Archilochus once said that under pressure, “We don’t rise to the level of our expectations. We fall to the level of our training.” OK, he wasn’t a driving instructor. He was a Greek poet from 650 BC. He’s not wrong though.

“When we get into a high-pressure situation, like coming face-to-face with a lion (not uncommon in Archilochus’ time and place), our bodies prioritize our blood flow to the parts of us that can help us either run away from or, the much worse option, fight the lion. We have a fixed amount of blood, so when more goes to our muscles, less goes to our brains. The prefrontal cortex (the part that does our higher-order thinking) takes the biggest hit. When facing a lion, we can afford to give up a bit of abstract thinking if it means we can run faster. But if you’re engaged in a task that requires complex analysis of a rapidly changing environment, that’s not so good.

“What does a long-dead poet and our prefrontal cortex have to do with turn signals in an emergency? Even though Archilochus didn’t know the science behind it, he correctly recognized that when confronted with a threat, we don’t think as clearly, and we’re going to depend more on our past practices. If you’re the kind of person who always uses your turn signals, there’s a good chance that in an emergency you’re going to instinctively use your signals without even realizing it.

“But if you don’t, have you broken the law? Eh, probably. The law states, in part, that “No person shall turn a vehicle or move right or left upon a roadway without giving an appropriate signal.” “There’s no clause indicating it doesn’t apply in emergency situations. However, the law also requires drivers to signal at least 100 feet before turning, and that’s likely not an option in an emergency. If it’s impossible to both comply with the law and avoid a crash, maybe the law doesn’t apply here, or, at least, that’s what I’d tell the judge.

“I have no enforcement authority, but I’m confident that the police are not going to get worked up about turn signal rules if you didn’t use your blinker while swerving to avoid a head-on collision. I’m so confident that I’ll buy a coffee for the first person who can send me evidence that they got an infraction for failing to signal while they were making an emergency maneuver to avoid a crash.

“Traffic laws aren’t suspended in the moments leading up to a potential crash, but when considering enforcement, police look at the totality of the circumstances. If you swerve to avoid a crash but don’t use your turn signal, an officer is under no obligation to take enforcement action.

“Let’s take Archilochus’ concept beyond turn signals to other safe driving behaviors, like scanning your surroundings, maintaining a safe following distance, checking your speed, identifying an escape route and minimizing distractions. If you practice them in low-pressure situations, they’ll be there for you in the critical moments.”

Another person asked Dahl whether using headlights during the day is any safer than using just the automatic running lights.

Dahl’s answer:

“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. (We need a punctuation mark for sarcasm.) The study by the National Highway Traffic Safety Administration was “not statistically significant.” However, several states did their own studies and reached similar conclusions to other countries: 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 daytime running lights. 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 U.S., they’re not required but available on many vehicles.

“Early complaints about DRLs (and driving with headlights on in the daytime) 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 5 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 daytime running lights, and I think it’s a big one, is that the system doesn’t light up any bulbs on the rear of the vehicle (at least with most cars.) As long as a driver remembers 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 haven’t seen the data to prove it, but 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. Daytime running lights 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 a driver who thinks 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%.”