The Capri program tracks when cars arrive on and leave campus, rewarding commuters with the chance to win money when they avoid rush hours. Modeled after a successful program in India, Prabhakar and research associates launched the Stanford version in April.
More than 2,000 people have already signed up for Capri, which stands for Congestion and Parking Relief Incentives. Depending on how frequently they side-step peak commute hours, commuters earn chances to win random cash amounts ranging from $2 to $50.
Unlike other Stanford programs that try to get people to leave their cars at home, Capri is designed for employees and students who drive, targeting those who have "A" or "C" parking permits. Some 12,000 people could participate, according to the university.
What might surprise people is the fact that a relatively small number of rush-hour commuters — 10 percent — can dramatically affect traffic, said Prabhakar, a professor of electrical engineering and computer science.
"The extra 10 percent drives it from small congestion to high congestion," Prabhakar said.
Thus, the amount of people in the program doesn't have to be high to make a difference.
To track cars, each Capri participant is given a radio-frequency identification tag (RFID) for his or her windshield. Much like with California's FasTrak system, gates around campus are equipped with scanners to detect the tags when cars pass by.
It's an idea that couldn't have been implemented without recent advances in technology, Prabhakar said.
"We have the technology for doing these things. It wasn't this easy 10 years ago," he said.
So far, it appears the program is working. By examining the flow of traffic, researchers have seen an increase in the number of people arriving on campus just before 8 a.m., the hour the peak commute officially begins, and leaving right after 6 p.m., after the evening commute hour ends.
"There's a fairly clear behavior shift," Prabhakar said.
His team is already devising ways to expand the program, creating a mobile-phone app that could substitute for the radio ID tag, and including bicyclists and walkers in the effort.
The program may stir fears of Big Brother watching over people's shoulders, but participation, even after signing on to the program, remains optional, Prabhakar said.
A commuter can remove the tag or turn off the app on any day he or she doesn't want to be tracked.
"The nice thing about incentives is you can do the good behavior but it ... puts the decision to share that behavior or make the behavior known on the commuter," he said.
When a "penalty" approach is taken to change behavior, such as catching solo drivers in the carpool lane, people simply try to hide their bad behavior.
Capri's system of rewards works on another principle, he said: "You let me know when you're doing the good behavior."
The project is funded by Stanford and a grant from the U.S. Department of Transportation, according to the university.