"You need to wait for a tow truck to come and move one of the hacked self-driving cars." "This is a concerning scenario, because when emergency vehicles want to get through, they can't," said Vivek. And when multiple vehicles are hacked, there is a critical slowdown, which can turn into complete stoppage. "Immediately after a vehicle is hacked, the traffic slows down around the hacked vehicle," said Vivek. So when the density of vehicles is very high, like during rush hour in Manhattan, small perturbations can have a ripple effect, producing traffic jams. In between is a unique, uber-connected state known as "synchronized flow," where the cars become highly correlated. When it's moving freely, it's like a liquid when it's at a standstill, it's like a solid-a state of complete blockage. Then the largest cluster of nodes experiences a growth surge, giving rise to uber-connectivity. The individual nodes in a random network form short-range connections gradually, until the system reaches a critical threshold. Cut off too many routes, and there won't be sufficient connectivity for cars to filter through. The more connected routes that are open, the more likely it is the water will filter through. Percolation theory is a mathematical model of a smooth, continuous phase transition (as opposed to a rapid one, like flicking a light switch), similar to water seeping through roasted ground coffee beans until it shifts into a new state: "coffee." Hot water seeping through packed coffee grains will hunt for the most viable path. If that reminds you of brewing coffee, that's exactly the right image. Vivek and his colleagues performed computer simulations of traffic flow in Manhattan, using a statistical method called percolation theory. And unlike compromised data, compromised vehicles can lead to physical injury.
Worst-case scenario: a small-scale hack affecting just ten percent of cars on the road would be sufficient to cause city-wide gridlock, essentially cutting half of Manhattan off from the rest of the city. Skanda Vivek, a postdoctoral researcher at Georgia Tech, described the study's findings at the American Physical Society's 2019 March meeting, held last week in Boston. That question inspired scientists at the Georgia Institute of Technology to quantify the likely impact of such a large-scale hack on traffic flow in New York City.
That poses a unique potential risk: if someone can hack one car, what happens if they manage to hack many at once in a major metropolitan city? Vehicles on the road will only have greater interconnectivity from this point forward, with self-driving cars on the horizon. In 2015, a pair of hackers demonstrated just how easy it was to break into the UConnect system of a Jeep Cherokee, remotely manipulating the speed, braking, steering, even shutting the car down entirely.