Hackers would only need to disable around one-tenth of cars in Manhattan’s rush-hour traffic to bring it to a standstill, physicists have calculated.

Cars are increasingly linked to the Internet and, like any computer, are vulnerable to hackers. To study the threat, Peter Yunker at the Georgia Institute of Technology, Atlanta, and his colleagues simulated the movement of cars in multi-lane traffic. The team modelled various densities of cars and proportions of vehicles that are suddenly and simultaneously disabled, as would happen in a hacker attack.

The likelihood that traffic would come to a complete stop was best predicted by the density of disabled vehicles, rather than overall traffic density, the researchers found. That’s because hacked cars could block every lane, which would stop even a light flow of traffic.

Using a model that factored in the degree of connectivity among Manhattan streets, the team found that disabling around 10% of vehicles in rush-hour traffic was enough to cause not only local jams, but also citywide disruption.

Manufacturers should use multiple independent wireless networks to connect different groups of vehicles in a city to the Internet, say the authors.