January 23, 2023

Three plus one (3+1) design philosophy for driverless cars

Brian Lathrop came up with a design philosophy for driverless cars – three plus one. The book Taming HAL: Designing Interfaces Beyond 2001 by Asaf Degani helped him come up with the philosophy. He is currently the Senior Principle Scientist at Volkswagen.

According to the philosophy, a driverless car has to get 4 things (3+1) right. These principles helps establish trust between the car and humans – drivers and pedestrians alike.

  1. The people (users, drivers, pedestrians etc) should know what mode the car is in at all times – whether it's driving itself of not.
  2. Coffee-Spilling Principle: We need to know what the car is going to do before it's actually done. There’s a screen that tells you what the next move will be—“left turn”—with a countdown timer until it happens.
  3. We need to know what the car is seeing. Driverless cars (eg. Tesla) show us a simulated map of the car's surroundings. The display tells us what the car is seeing.
  4. We need a perfectly clear transition when a car takes control or when we take control from the car.

Some of these principles also map back to the Usability Heuristics we use in Product and UX Design. For eg. visibility of system status, user control and freedom.

These rules also remind me of Isaac Asimov's Three Laws of Robotics popularised by the Will Smith movie I, Robot.

  • A robot may not injure a human being or, through inaction, allow a human being to come to harm (eg. driverless cars taking control when they sense driver is asleep or distracted)
  • A robot must obey the orders given it by human beings except where such orders would conflict with the First Law
  • A robot must protect its own existence as long as such protection does not conflict with the First or Second Laws


  • User Friendly (Cliff Kuang, Robert Fabricant), Chapter 4: Trust