As Google works towards the dream of the total driverless car, one of the problems that has been cropping up is that the vehicles are, by design, very defensive drivers. This can leave them stuck at four-way intersections where a little bit of aggression is required before other cars will make space on the road. It can throw off the humans around them, who are prone to rear-ending a vehicle that stops a little too courteously. And it can result in speeding tickets for, well, driving too slow.

Earlier this week Google received a patent that lays out some of its ideas for how driverless cars might communicate with the pedestrians around them, allowing the vehicles to broadcast their intentions without being overly aggressive. For example a flashing stop sign on the side door would let humans know when not to cross the street in front of the car. A sign on the front bumper could flash when it was safe to pass in front of the car. And a robotic hand could give the kind of signals to fellow motorists they often look for from other humans.

The CEO of Ford recently offered the aggressive predication that fully autonomous cars would be on the road in four years. Tesla has already begun offering some fairly advanced self-driving features, adding them onto cars already on the road through an over-the-air software update. Regulators are somewhat at a loss about how to handle this rapidly expanding technology. But companies like Google know that even a single accident or fatality early on in the deployment of autonomous vehicles could set the while industry back years, and so it's taking every step possible to build cars that can keep passengers, other drivers, and even pedestrians completely out of danger. No word yet on the policy for flipping the bird.