Credit: Nissan

I recently learned of a rather interesting pilot study undertaken by Nissan together with the Contra Costa Transportation Authority and UC Berkeley that leverages the automaker's partially automated driving system, ProPilot Assist, to ease traffic congestion. The idea is called "Cooperative Congestion Management," which works by letting a car in traffic inform vehicles behind it.

Researchers from Nissan's advanced technology center in Silicon Valley have trialed CCM on I-680 in the Bay Area, logging about 600 miles. Starting with Nissan vehicles equipped with ProPilot Assist, which combines adaptive cruise control and lane keeping, they added the ability for those cars to communicate with each other, informing other cars about their speed and any hazards. On the road, they were able to show that the system reduced hard-braking events by 85 percent and cut time stationary in traffic by 70 percent.

But we're not talking about platooning—the idea of having road trains of autonomously driven semi trucks networked together and driving in convoy was all the rage a decade ago, but mostly fell from favor once people realized the human truck drivers were needed for more than just the steering, accelerating, and braking bits of the job.

Also, this is not just another demonstration of V2V, the stalled-out system that was supposed to use Dedicated Short-Range Communication (DSRC) radios so cars could talk to other cars. Automakers might have settled on that spec in the early 2000s, but they never bothered actually building it into any cars, and in 2022 the FCC won a court battle to reassign that part of the electromagnetic spectrum to someone who might actually use it.

Instead, CCM works by having a lead car, or "probe," send information to following CCM-equipped cars, which are separated by non-CCM cars between them. The information from the probe car lets the following cars keep an appropriate distance from each other—between 30 and 60 seconds—and if there's a slow down ahead, the following cars will decelerate more gently over time, preventing the kind of concertina action that triggers traffic jams when human drivers see someone slowing down in front of them.

Jerry Chou, a senior researcher at Nissan's Silicon Valley center, described CCM to me as "mixed autonomy—that means a mix of the controlled vehicles and other human driven vehicles in between." Instead of DSRC, the cars use their embedded LTE modems to communicate via Nissan's cloud.

As most people who have used adaptive cruise control know, if your following distance is too large, other drivers will often cut in, causing you to decelerate. "So we did spend some time to balance this phenomenon and the performance of our system. So there's some parameters we continue to control to balance this," Chou told me.

Note the test equipment that's fitted to the dash of this CCM-equipped Nissan Ariya test vehicle.
Credit: Nissan

Next, I asked Chou what percentage of cars in traffic would need to be CCM-enabled to effect a reduction in congestion?

"So in our simulations we tried different penetration rates... and we saw that our benefits increase proportionally to penetration rates. But we already can see some good results at around 4-5 percent penetration," Chou told me. "But you know, that's actually one challenge of experimental. Since our experiment only has a few cars, we have been thinking about how to control just these few cars to see some results."

Future refinements for the system include giving the humans some feedback on why their cars are slowing (in part so they don't countermand the system and just accelerate manually). If that proves successful, we may even see CCM licensed to other automakers in the future, Chou said.