In a driver-less future, all cars communicate their intents to other nearby cars, stopping on a highway will be as safe as pulling over on a shoulder is today. It will feel dangerous, and it will be unsettling knowing cars are passing you by at speed, but the driver-less aspect of all cars ensures a high degree of safety.

That would be the result in the long term. But in this transition period TO driverless cars, I agree that stopping on the highway in your driver-less car is a big no-no.

I believe car-to-car communication and auto-slowing-down based on that will come much sooner than driverless cars (US regulators are already talking about making V2V communications mandatory by 2017), so by the time the first driverless cars are sold, it'll probably be reasonably safe to slow down on the highway.