Why We Need a Fourth Traffic Light

If there were a religion based on road markings, their Bible would be the text of the 1968 “Vienna Convention on Road Signs and Signals,” and their Holy Trinity would be the three illuminated components of the standard traffic light: the Red Light, the Yellow Light, and the Green Light — three separate entities, and yet still one whole, the traffic light itself. Well, now researchers at North Carolina State University have proposed a new fourth light for the standard traffic light — a white light, and its usage would be tied to automated vehicles.

Actually, the current announcement is actually an expansion of the original quartet of lights-proposal from February of last year, but this new one factors in pedestrian traffic as well. With 66% of drivers reporting they’re afraid of self-driving cars, it’s not unreasonable to think that one reason is a lack of understanding what an autonomous car might do. The fourth light is designed to help bridge this gap.

Think of it this way: You’re in a regular, non-self-driving car. You pull up to a traffic light at a typical four-way intersection hoping to turn right and there are three self-driving cars in front of you. To make things more complex, there’s also a guy pushing a stroller to your right hoping to cross the street. In a normal situation with no self-driving cars you’d know what’s likely to happen. But what about a situation where many of the cars can speak to one another? In theory, those connected cars could behave differently and more efficiently except… you aren’t a connected car and neither is the pedestrian.

Essentially, the new white light would be used in conjunction with 1. automated, self-driving vehicles with the ability to communicate with other automated vehicles and traffic signal control computers, and 2. human-driven vehicles with similar car-to-car and car-to-infrastructure communication abilities.

Here’s how Ali Hajbabaie, co-author of the paper and an associate professor of civil, construction and environmental engineering at NC State University, describes the concept:

“Our earlier work introduced the idea of a fourth traffic signal called a ‘white phase,’ which taps into the computing power of autonomous vehicles (AVs) in order to expedite traffic at intersections – but we had not yet incorporated what this concept would mean for pedestrians. We’ve now expanded our computational modeling to account for foot traffic, and the results are extremely promising for both pedestrians and vehicles.”

To understand what these papers propose, let’s look at what they mean by the “white phase,” which presupposes the existence of automated vehicles that are capable of communication with one another and traffic light signaling systems. For this to be effective, there would need to be a critical mass of these vehicles, along with human-driven vehicles able to connect to the same networks as the automated ones, and neither of these categories of vehicles are here yet.

Here’s how the abstract to the original paper explains the “white phase,” which is not referring to that summer you swore to only wear alabaster or pearl:

This study presents a vehicle-level distributed coordination strategy to control a mixed traffic stream of connected automated vehicles (CAVs) and connected human-driven vehicles (CHVs) through signalized intersections. We use CAVs as mobile traffic controllers during a newly introduced “white phase”, during which CAVs will negotiate the right-of-way to lead a group of CHVs while CHVs must follow their immediate front vehicle. The white phase will not be activated under low CAV penetration rates, where vehicles must wait for green signals.

Essentially, it works like this: Connected automated vehicles are talking to one another and to traffic lights, and when they all compute an ideal, optimized traffic flow pattern, they can group together and take control of the traffic through an intersection by triggering the white light, which would tell human drivers to just follow the vehicle in front of them through the intersection, which can reduce traffic delays by a pretty wildly varying amount, from 3.2% to 94.06%.

The study also claims a 40.2% to 98.9% reduction in total delay compared to a “fully-actuated signal control obtained from a state-of-practice traffic signal optimization software.”

So, what do we make of this fourth traffic light? Essentially, this light indicates that some interconnected group of automated cars is taking over traffic flow patterns at that intersection, and human-driven cars should follow.

According to Hajbabaie again,

“Our previous research found that the more AVs there are on the road, the more efficiently the traffic moves,” Hajbabaie says. “To be clear, this improves travel time, fuel efficiency and safety for all of the cars on the road – not just AVs.”

I have no doubt that the mathematical models used for this study do in fact show that traffic can flow better and easier with fleets of AVs evaluating things and talking to one another. But, the issue here is that in the actual, real, grimy world we live in, so far the companies working on automated vehicles do not appear to be focused on developing common vehicle-to-vehicle (V2V) communication standards necessary for this to work. This lack of progress on universal V2V has been noted before by far more reputable sources than myself.

For this fourth light to actually make sense, a lot has to happen. We need more automated vehicles, a lot more, and we need a car-to-car communication standard and much wider-spread car-to-traffic-light-systems, sort of similar to what Audi uses for their Traffic Light Information system.

I don’t think this white light will be added anytime soon, because for it to make any sense, we’d need large numbers of AVs and a comprehensive and widely accepted car-to-car communication system, and we’re just not there yet. It’s a good idea for finding a way to incorporate human-driven cars into the traffic flow optimizations of AVs in a relatively low-cost, well-understood way (people know to pay attention at traffic lights, and the only rule, follow the car ahead of you, is easy enough to convey) so in that sense I think the white light is a smart plan.

Oh, and if you don’t like a white light, the authors of the study are understanding:

“And, just to be clear, the color of the ‘white light’ doesn’t matter. What’s important is that there be a signal that is clearly identifiable by drivers.”

Yeah, it should be something other than white. How about ivory? Or eggshell?

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