I always wonder what would have happened if humanity had invested in conveyor belts instead of cars and roads for the last 100 years.
I can't shake away the sensation that it could have been a better call.
When I first read that book, I thought it seemed like a lot of wasted space because of the amount of parallel lanes you would need to achieve highway speeds. Then I started driving and noticed how wide our highways already are.
I don't recall the same setup in the I, Robot stories (but it's been a long time).
We might not have conveyor belts for roads, but we are defiantly living in the future.
To your comment, yes, that is pretty amazing, to have my (our) intelligence augmented in this way. Because just writing it down, and reading it once, is not sufficient to remember it.
It took us a long time to understand the power of writing, and it could be that eventual understanding of the power of search will also have vast implications.
Luckily, Wikipedia has our backs on this, with a convenient list of works containing moving walkways: http://en.wikipedia.org/wiki/Moving_walkway#Science_fiction
Several of Heinlein's other Future History books and stories reference the rolling roads.
These are without a doubt my favourite of Asimov's books :)
Earth has evolved to a point where the population lives in Cities (capitalisation is important!) -- massive, hundreds of square miles completely enclosed with no outside areas at all. They might as well be space stations.
Transit within these cities takes place on 'strips' for local transport -- think of them as 'lanes' on a freeway. The first strip you step on to is an acceleration strip (onramp), which gets you up to speed to then step onto faster strips.
There's also an "Expressway", which is basically a metro, which you step onto from the fastest strip (I think there is an acceleration strip too) which takes over when you want to go longer distances.
Then for even longer distances you have aircars (planes!).
It's a really good system, but only for highly, highly urbanised areas. I think there's only 2 or 3 cities on the planet at the moment truly dense enough. New York, and perhaps central London.
Then, of course, if your conveyor belt is pedestrian-based, you have exposure to the elements (also meaning limited long-distance travel due to slow speed) and switching between conveyors would be troublesome (particularly if you're inform or have baggage). If you instead ride in some sort of pod, you can up the speed and protect yourself from the elements, but you still need to get it on and off the conveyor belt smoothly; it's be something approaching the complexity of a car anyway. How also would you prioritise/speed up emergency vehicle traffic, which often has to go as quickly as possible?
It's certainly an interesting thought experiment, coming up with the pros and cons.
You assume that there was a call. Modern roads are just a long series of small, natural, incremental progressions on, essentially, a beaten path through the woods. Many of them are probably even in much the same places.
Cars are much the same. First, crude carts, then progressively bigger carts drawn by progressively bigger animals, then someone builds an "artificial animal", put it inside the car and so on.
There has been some non-continuous breaks, the most notable one is the railroad which present a new set of benefits and challenges. The biggest challenge is that railroads require exclusivity in usage (different kinds of road users can share the road, ultimately by temporarily stepping off the road) which is very difficult to allow without central planning. And central planning is really, really difficult.