A study is underway in Japan to build dedicated lanes for self-driving cars.

There have been experiments with dedicated lanes in the past, including a special automated lane back in the 90s in San Diego. The problem is much easier to solve (close to trivial by today's standards) if you have a dedicated lane, but this violates the first rule of robocars in my book -- don't change the infrastructure.

Aside from the huge cost of building the dedicated lanes, once you have built a lane you now have a car which can only drive itself in that dedicated lane. That's a lot less valuable to the customer, effecitvely you are only get customers who happen to commute on that particular route, rather than being attractive to everybody. And you can't self-drive on the way to or from the highway, so it is not clear what they mean when they say the driver sets a destination, other than perhaps the planned exit.

Yes, the car is a lot cheaper but this is a false economy. Robocar sensors are very expensive today but Moore's law and volume will make them cheaper and cheaper over time. Highway lanes are not on any Moore's law curve, in fact they are getting more expensive with time. And if the lane is dedicated, that has a number of advantages, though it comes with a huge cost.

Of course, today, nobody has a robocar safe enough to sell to consumers for public streets. But I think that by the early 2020s, when this study might recommend completing a highway, the engineers would open up the new lane and find that while it's attractive for its regular nature and especially attractive if it is restricted and thus has lighter and more regular traffic, the cars are already able to drive on the regular lanes just fine.

A better proposal, once robocars start to grow in popularity, would be to open robocar lanes during rush hour, like carpool lanes. These lanes would not be anything special, though they would feature a few things to make the car's job easier, such as well maintained markings, magnets in the road if desired, no changes in signage or construction without advance notice etc. But most of all they would be restricted during rush hour so that cars could take advantage of the smooth flow and predictable times that would come with all cars being self-driving. Unless humans kept taking over the cars and braking when they got scared or wanted to look at an accident in the other lanes, these lanes would be metered and remain free of traffic jams. However, you need enough robocar flow to justify them since if you only use half the capacity of a lane it is wasteful. On the other hand, such lanes could be driven by the more common "super cruise" style cars that just do lane following and ACC.