In theory, the best way to maximize traffic flow along busy urban streets is to coordinate the series of traffic signals that drivers encounter. In practice, that’s far easier said than done. But with the completion of recent research supported by the Texas A&M Transportation Institute (TTI), traffic engineers are a big step closer to that lofty aspiration.
Under a subcontract, TTI’s work on the project — Traffic Optimization for Signalized Corridors (TOSCo) — was led by TTI Senior Research Engineer Kevin Balke. The work was sponsored by the Federal Highway Administration and accomplished by the Collision Avoidance Metrics Partners LLC through a consortium of automakers that includes Honda, Ford, Nissan, Hyundai, General Motors and Volkswagen. IAV GmbH, a Germany-based engineering firm, also assisted in system development and integration.
The TOSCo system involves a series of applications using wireless communications from both the infrastructure and connected vehicles to optimize traffic flow on signalized arterial thoroughfares. The system considers the length of each queue of vehicles and the time remaining in each green or red phase, along with other factors. This information is sent to approaching connected vehicles 10 times per second, enabling strings of vehicles to determine and adjust to optimal speeds, proceed en masse, and minimize the likelihood of stopping.
If stopping is unavoidable, the waiting TOSCo vehicles will launch collectively when the signal turns green, keeping the vehicle string intact. By keeping the vehicles in close proximity to each other as they launch on green, the system can maximize the count of vehicles proceeding through the intersection. The TOSCo system works with the vehicle’s cooperative adaptive cruise control function, and the driver can take control at any time.
“I like to call it next-generation cruise control,” Balke says. “It’s very difficult to build new capacity in roadways, so we’re trying to eke out as much capacity in the system as we can possibly get through these advanced technology projects.”
The TOSCo work began in 2015 with concept development, followed by simulation models focused on vehicles, infrastructure and performance, along Plymouth Road in Ann Arbor, MI, and SH 105 in Conroe, TX.
Outcomes from the simulations showed significant benefits. Results showed substantial reductions in stop delays and the number of stops along both the low-speed Ann Arbor corridor (40 percent decrease) and the high-speed Conroe corridor (80 percent decrease). Similar reductions in the total number of stops were recorded along both corridors. The TOSCo system did not cause substantial changes in total delay for travelers, and travel times and speed were not significantly affected.
Because average speeds were not affected in the simulations, there was no substantial impact on vehicle emissions or fuel consumption, although the TOSCo system did produce minor reductions in hydrocarbons and nitrogen oxide.
In a second phase of the work, researchers built a closed-course test site on the Texas A&M-RELLIS campus at TTI. Favorable results from the simulations enabled researchers to fine-tune the system there before proceeding to a real-world deployment on FM 1960 in Houston in spring 2022.
“We run the scenarios on the test track, we come back and analyze the data, and we see if there’s any room for improvement so the system can perform better,” says Shah Hussain, a system architect at Ford Motor Company. “Then we go back to the test track, and we do the same process again and again. It’s quite exciting and fun to watch things perform exactly as we expect from what we see in the simulations.”
Like many other mobility enhancement efforts, TOSCo intends to maximize the usefulness of existing infrastructure — a goal underscored by industry partners on the project.
“It’s going to come to a point where we cannot build our way out of congestion; there’s only limited space to put in new roads,” says Roy Goudy, the project’s principal investigator and a senior principal engineer at Nissan. “So in order to deal with our growth, we’ll have to rely on technological solutions to improve our transportation network mobility, our fuel economy and our emissions reduction efforts.”