At roughly $125 to install, a Sensor Confirmation Indicator is among the least expensive infrastructure investments a city can make. Nothing more than a bright blue LED attached to the side of a traffic signal or mounted on a light pole, it performs the most basic function imaginable, lighting up when a bike, car or other vehicle is detected by a sensor loop or traffic camera. The Indicator gives no instructions, and makes no prohibitions. It just lights up when approached. That’s it.

And yet, as someone who’s encountered such indicators, I can attest that the experience of being detected by one while biking is profound. Perhaps because so much infrastructure is so indifferent to bicycles, discovering a piece that responds to your presence feels a bit like having the bronze statue in a memorial open its eyes and greet you by name. This tiny blue light fundamentally alters your role in the intersection’s conversation, elevating you from an unwelcome nuisance to an active participant.

The intersection of Northeast Morris and Northeast Martin Luther King in Portland is part of my daily bike commute, and like most of the other eight Sensor Confirmation Indicator locations in the city, it was chosen because a busy bike route (NE Morris) crosses a major arterial road (NE MLK) there. I’ve not once seen a driver or cyclist run that light since the Indicators went in, nor at any of the other locations. According to Peter Koonce, the head signals engineer for the Portland Bureau of Transportation (PBOT), studies at Portland State University confirm that red light compliance among people on bikes has increased significantly at every one of the nine locations.

The intersection of North Interstate and NE Oregon

The intersection of N Interstate and NE Oregon. That’s I-5 to the right, and yes, a garden in the shape of a peace sign in the lower left.

Of those intersections, the one at North Interstate and NE Oregon is worth particular scrutiny. For one thing, it’s hosting an unusually complicated conversation. A one-way street carrying car traffic off the Steel Bridge meets Interstate Avenue, a major two-way arterial that feeds into a nearby Transit Center, as well as the arena where the Portland Trailblazers play. It also absorbs heavy bike traffic from three different separated bike paths that rejoin the grid at that point.

And yet, the intersection has a stellar safety record, as well as a red light compliance rate of 99.4 percent among people riding bikes, making it perhaps the most respected traffic signal in all of North America.

The Sensor Confirmation Indicator light certainly contributes to the intersection’s success, but it’s actually a small part of the story. The bike traffic that flows onto the road there, for example, gets its own phase in the signal cycle, allowing it to cross diagonally from path to on-street bike lane in a single motion, an unusual movement that’s clearly indicated by pavement markings and dedicated signage. This diagonal phase is controlled with a traffic signal using bike-shaped stencils over the red, yellow and green lights, an innovation that’s been embraced in several US cities, despite appearing nowhere in the AASHTO “Green Book” that governs most American street design. And the blue LED mounted next to that signal is linked to a small sensor loop buried not in the asphalt, but in the sidewalk ramp where bikes naturally queue up. It sounds like a lot of fussy detail, and it is, but no more than what’s already been installed for cars at thousands of comparable intersections.

Despite the best efforts of engineers, traffic cops and conscientious road users, things still go wrong on American roads far too often, costing us over 30,000 lives a year, to say nothing of the injuries and the monetary loss.

Traffic deaths weigh heavily on the US compared to other wealthy nations, and the culprits are many. Our licensing standards are laughably low, criminal prosecution of aggressive drivers is scant, and the structure of our cities encourages average citizens to drive vast distances as a matter of habit. To think that a cheap technological fix like a blue LED could seriously impact this tragic status quo is naive at best.

Yet things are getting better. It’s safer to travel on a US street now than at any point since we started keeping records, regardless of which mode you’re using. We owe a lot of this improvement to better safety features in cars, and to more skilled emergency medical care, but we also owe it to better designed streets. Much of what makes an urban street look different than it did 10 or 20 years ago stems from an improved understanding of why people behave the way they do. We once relied on speed limits and radar guns to slow cars down; now we know that a curb bumpout or traffic circle can do the same job more effectively. Broadly speaking, we’ve learned that our actions are largely (though not entirely) a response to our environment, and many “innate” behaviors are actually design problems. The complex conversation proceeds at every intersection, and while we can’t tell people what to say, we can set the tone and choose how to respond.

This is what’s so heartening about the Sensor Confirmation Indicator, and the dozens of other small, thoughtful infrastructure elements that have begun appearing on America’s streets. The blue LED speaks with a whisper that could be easily lost in a noisy conversation, but it whispers exactly the right thing. In the middle of the chaotic miracle of modern traffic, it recognizes that the first step to predictability is acknowledgement. And rather than shout another directive, it simply offers confirmation: you are heard, you are part of this, this is for you.