For as ear-piercing as ambulance sirens are, you’d think they’d be better alert systems. Truth is: they’re shockingly ineffective. Drivers register the sound only at close proximity and at very low speeds. Guessing from which direction the ambulance will appear is always tricky, too—especially when the new Daft Punk is turned up really loud. In fact, a recent study found that visual cues—rather than audio ones—account for 90 percent of how regular ol’ drivers register the presence of an ambulance on the road. So when ambulances need to get drivers out of the way quickly, it’s lights—not sirens—that are truly effective.


In the history of mobile emergency signaling, lights were a late addition. When New York City launched its first ambulance service in 1869, the horse-drawn vehicles sounded a gong to get folks (traveling around four miles per hour) to pull over. In 1909, the Albany-based James Cunningham, Son & Company launched the first commercial gas-powered auto ambulance, but its specialized lighting was on the interior, in the form of a few domed lamps used to illuminate the ill.


Because there weren’t any federal standards for the light-based alert until the early 1970s, its earliest history is muddy. If you wanted an ambulance, you’d work with a manufacturer to outfit it based on your preferences—so there was a lot of variation. For a long time, hearses served double duty as ambulances, moonlighting to carrying the living sick, as well. While some models had three lights affixed above the windshield, for a long time that was as far as ambulance lights went.

Other hearses were designed to transform into full-fledged ambulances in a moment’s notice. Some of Buick’s adaptable models from the late 40s and early 50s had a side-hinged hood, which allowed owners to pull off a somber front and replace it with an ambulance fitting, complete with two front-facing emergency lights. And Chevy modded their own emergency signal. On a model from 1965, the manufacturer slapped some tail lights above the windshield to achieve the desired get out of the way! effect.

Image via Pontiacs Online .

Still, ambulances were kind of all over the place, without regulation or oversight. A government report from 1978 lamented the disorganization: “Until the present time, the acquisition of emergency signaling equipment has been largely a haphazard procedure.” Every state seemed to have its own standards. Alaska preferred that three sides of its emergency vehicles were outfitted with something flashing and red; Colorado was into the same color, but only required that it be visible from the front and rear. Another state preferred only blue lights on ambulances, while another 39 states prohibited them.


But that wasn’t all. The standards for “authorized emergency vehicles” stretched waaaay beyond emergency vehicles, expanding to include pet ambulances, sanitation and pest-abatement trucks, and in some cases, even doctors’ personal vehicles. Maybe—just maybe—there should be some national agreement about the type, color, and number of lights gaining in the rear view. Sending a clearer signal, the report concluded, would improve driver reaction time, not to mention the safety of those manning the ambulances.


Fast forward 35 years, and the strobe type, colors, and quantity of lights on ambulances are still all over the place. In Minnesota, blue lights are prohibited on everything but snowplows and road maintenance vehicles; In Illinois, all medical and fire emergency vehicles use the proverbial blues. The federal government standardizes a minimum, but for the most part, each state still maintains its own system, unique enough to provide a strange game of state-by-state travel bingo.

But if the purpose of all those lights is to get the attention of the humans, why don’t we tailor the color, coverage, and flash rate to what’s best for the target audience? According to Michael Flannagan, an associate professor who works at the University of Michigan’s Transportation Research Institute, part of the problem is establishing an empirical best practice. What they do know: “Feelings of being bothered [by ambulance lights] are certainly real,” Flannagan explains. But turning that information into policy change—say, by lowering the intensity of emergency lights at night—requires a more rigorously supported argument. Even though people report the lights can be distracting, Flannagan says, “We can’t establish that there’s an objective safety problem.”


So researchers like Flannagan have chipped away at the problem from a different angle, by conducting studies testing which colors are most visible in daytime and nighttime hours. The take away, according to Flannagan, is that “Blue is good all the time—better than you might expect.” In fact, our eyes are more sensitive to blue than white or red—especially after it gets dark. As night sets in, rod receptors in our retinas are more sensitive to blue’s short waves compared yellow’s medium waves and to the red’s long waves, even though a photometer might read the intensity of the three the same. (Perhaps—ahem Minnesota—it shouldn’t be wasted on just snowplows.)


Finding a balance between alerting drivers without needlessly distracting them could be a matter of fine-tuning brightness based on context cues, like the time of day or the weather conditions. For example, turning the white up during the day would help, as would lowering all the lights’ intensity at night, when drivers are quicker to notice the flashing behind them. But until we develop the infrastructure and technology needed to standardize a responsive system, it looks like we’re stuck with the disorganization we inherited from the 1970s. So turn the music up, keep your eyes peeled, and hope that those flashing lights behind you don’t come with a ticket.