Mini roads for robocars
At the positive end of my prediction that robocars will enable people to travel in "the right vehicle for the trip" and given that most trips are short urban ones, it follows that most robocars, if we are efficient, will be small light vehicles meant for 1-2 people, with a lesser number of larger ones for 4-5 people. 2 person cars can even be face to face, allowing them to be under 5' wide, though larger ones will be as wide as today's cars, with some number as big as vans, RVs and buses.
Small, lightweight vehicles are not just greener than transit, they also require far less expensive road. While the initial attraction of robocars is that they can provide private, automated, efficient transportation without any new infrastructure, eventually we will begin building new development with robocars in mind. Various estimates I have seen for multi-use paths suitable for people, bikes and golf carts range around $100K to $200K per mile, though I have heard of projects which, thanks to the wonders of government contracting, soar up to $1M per mile. On the other hand, typical urban streets cost $2M to $3M per mile, an order of magnitude more.
Consider a residential robocar block. It might well be served by a single 10' lightweight use lane. That lane might run along the backs of the houses -- such back alley approaches are found in a number of cities, and people love them since the garage (if there is one) does not dominate the front of your home. It might also be in the front of the house. New construction could go either way. Existing areas might decide to reclaim their street into a block park or more land for the homeowners, with a robocar street, sidewalk and bike path where the road used to be.
We only need a single lane in one direction on most streets, though the desire to get 8' wide vehicles in means there would be 2 lanes for the narrow vehicles. The lane would have no specific direction, rather it would be controlled by a local computer, which would tell incoming vehicles from which direction to enter the lane and command waiting vehicles to get out of the way. Small wider spots or other temporary holding spots would readily allow cars to pass through even if another vehicle is doing something.
You would not need a garage for your robocar as you can store it anywhere nearby that you can find space, or hire it out when you don't need it. You might not even own any robocar, in which case you certainly don't need a garage to store one. However, you probably will want a "delivery room," which is something like a garage which has a driveway up to it. Deliverbots could use this room -- they would be given the code to open the door -- to drop off deliveries for you in a protected place. You could also have the "room of requirement" I describe in the deliverbots page.
This plan leaves out one important thing -- heavy vehicles. We still need occasional heavy vehicles. They will deliver large and heavy items to our houses, ranging from hot tubs to grand pianos. But even heavier are the construction machines used in home construction and renovation, ranging from cranes to earth movers. How can they come in, when their weight would tear up a light-duty road?
The answer is, not surprisingly, in robotics. The heavy trucks, driven by robots, will be able to place their tires quiet precisely. We can engineer our robocar paths to include two heavy duty strips with deeper foundations and stronger asphalt, able to take the load.
Alternately, since the tires of the trucks will be further apart than our robocars, they might just run their tires on either side of a more narrow path, essentially on the shoulders of the path. These shoulders could be made not from heavy duty materials, but from cheap ones, like gravel or dirt. The trucks would move only very slowly on these residential blocks. If they did disturb things there, repair would be easy, and in fact it's not too much of a stretch to predict either a road repair robot or a small road repair truck with a construction worker which moves in when problems are detected.
The volume of heavy trucks can be controlled, and their frequency. Their use can be avoided in most cases in times when the pavement is more fragile, such as when the ground is soaked or freezing. If they do damage the road, repair can be done swiftly -- but in fact robocars can also be programmed to both go slowly in such alleys (as they already would) and avoid any potholes until the gravel robot fills them. Robocars will be laser scanning the road surface ahead of them at all times to avoid such things in other areas.
I keep coming up with dramatic savings that robocars offer, and the numbers, already in the trillions of dollars and gigatons of CO2 seem amazing, but this is another one. Urban "local roads" are 15% of all U.S. road mileage, and rural local roads are 54%. (There are just over 2.6 million paved road-miles in the USA.) To add to the value, road construction and asphalt are major greenhouse gas sources.
To extend this further, I speculate on what might happen if small robocars had legs, like BigDog.