These came into my mind a few years back as a way to keep vehicles further away from each other on the highway thereby making it more obvious when vehicles merge into other lanes. In other words it’s a way of visually warning drivers that you’re merging into their lane (because 99% of drivers are bastards who don’t use turn signals or ignore other drivers using them) and it’s also harder to cut someone off or accidentally drift into their lane. Vehicles can use the gutters to signal that they are changing lanes by driving one tire in the gutter so your vehicle stand out from the others and lets drivers know you are preparing to enter their lane. It also might have a psychological effect on drivers, making them more likely to stay in their lane and less likely to merge around (which is what causes random traffic backups [traffic waves]).
Pretty self explanitory. The disadvantages however are significant. It takes 4 normal lanes to create 3 “spaced” lanes. So you loose 1 lane of traffic. So right off the bat this boils down to a safety vs capacity issue.
The second problem is this. The lanes space out traffic more, thus giving drivers a safer feeling. And this “safe feeling” goes against the “Risk Compensation Effect” (the safer and more protective you make something the more risky and careless people become because they no longer think it’s a threat. Real world examples: Drivers who know they have anti-lock breaks drive more aggressively, bikers who wear helmets bike faster, habitually unbelted drivers drove faster and more carelessly when they put on their seat belts, children who wear protective equipment are more likely to take risks, and cities with smoother roads and clearer lane markings have more accidents.) So drivers might get used to the feeling of safety and be less cautious to other vehicles merging into their lane abruptly.
It might benefit high speed 2 lane highways in the US. Where the posted speed limit is 80 or 85 (drivers add on 10-15 mph) and drivers speed at about 95 miles an hour. In that case you would want drivers to stay further away from each other. But again, the well proven “risk compensation effect” might work against us and the lane spacers might actually increase the accident rate. Drivers might get a false sense of safety and become careless drones who ignore others merging into their lane.
I don’t know. But for anyone who wants to try it, here it is.