In theory, driving mainly consists of looking through glass, turning a wheel, and putting pressure on one of two pedals. But, as everyone knows, in practice, driving means swerving to avoid tires on freeways, slamming on brakes to escape collisions, waving with your hand to signal to the driver at the stop sign to please, just go first. (I know we both got to the line at the same time. Seriously, you go. No? Not going to go? Fine, I'll go. Oh – nevermind, now you're going. Really?)

So it's not really a surprise that intelligent, rational self-driving cars have difficulty on streets overcrowded with irrational, hubristic humans. Most significantly, self-driving cars will have to be able to drive on city streets teeming with pedestrians. If pedestrian-automotive relations already seem bad, imagine trying to jaywalk in a city filled with robo-cabs.

To deal with this, Google has patented a slew of new ideas, including a "physical signalling system" that would comprise some kind of mechanical arm. Other ideas include a stop sign attached to the car, a flashing symbol like existing crosswalk signs, or even having the car make noises.

As Google rightly notes in the patent application, "Simply stopping a vehicle without these driver-initiated signals may not be sufficiently reassuring to the pedestrian that it is indeed safe to cross."

Related:

• Think driverless cars will reduce traffic? Not so fast.
• The "algorithmic dreams" of driverless cars, and how they might affect real-world urban design
• Is America actually shifting away from its car obsession? Not entirely.
• Car-free events significantly improve air quality
• Dawn of the self-driving car: testing out Tesla's autopilot function