In the future, cars and buses will be powered like laptop computers. Sometimes, they will run on batteries that will supply electric power to run the vehicle for short periods of time disconnected from the power grid. Sometimes, they will operate connected to the power grid and get their power from there.
Existing batteries are capable of powering electric cars which are identical in all respects but one, range, to existing internal combustion vehicles. But while a typical car or truck has a range of about 300 miles on a single refueling, a comparable electric vehicle can only go 40 to 100 miles on a single night's charge. Many people have assumed, as a result, that this will limit personal vehicles to intracity traffic unless a better battery is invented. But this doesn't have to be the case.
Electric vehicles are fine for light intracity travel. My average daily driving is about 16 miles a day, and my home garage already has plugs connected to the power grid that I could use to use to recharge it in the evenings. My bookkeeper drives more than I do, an average of 70 miles a day, but could also probably manage typical daily intracity driving completely on battery power.
But suppose I want to commute from Colorado Springs to Denver, or travel to Vail for the weekend? How do I plug in then?
The technology necessary to do this is more than a century old and is used today in street cars and in the Northeast Corridor's Amtrak service. The vehicle is connected to an Overhead Catenary, which is a system of overhead wires used to supply electricity to a vehicle equipped with a pantograph.
Historically, we have only equipped locomotives and street cars with pantographs, but this wouldn't have to stay that way. A car or bus can be equipped with a simple guidance system, that is a part of the pantograph-caternary system that keeps the vehicle traveling in line with the overhead wires on a road without tracks.
The place it makes the most sense to do this is on interstate highways. Many passenger rail plans already call for using the same basic routes as interstate highways. The vast majority of the people in the United States live within 30 miles of an interstate highway. A large share of intercity traffic takes place on interstate highways, but interstate highways make up only a small share of all roads in linear miles. The limited access nature of these highways makes them attractive places to use guidance systems that keep vehicles in line with the overhead wires powering them. Constant maneuvering from lane to lane isn't necessary on most long haul trips (hence, we have cruise control as a common feature in cars for highway driving). Many interstates either have or have planned high occupancy vehicle lanes which already favor buses and would be perfect places to add an overhead catenary. Many interstate highways are also already paralleled by high voltage power lines. Because the only upgrades necessary to the highways would be a set of overhead wires, and vehicles are designed with the height limitations of interstate highways in mind, adding an overhead caternary system would not prevent conventional internal combustion vehicles from sharing the road with electrically powered vehicles with pantographs during the transition period.
Interstate highways generally operate at or near the speed of existing passenger rail in the United States. They already connect most major cities, have systems in place to maintain them, and are already built, so no major new right of ways would have to be acquired.
Adding overhead catenary wires to existing interstate highways would be much less expensive than building new passenger rail tracks. I've heard estimates of $1 million a mile to put in streetcar lines on existing streets (far less than most kinds of rail and essentially what Denver has downtown). But it would be cheaper per mile to add overhead catenary wires without embedding rails flush with the street, and it would also probably be easier and cheaper to do the bulk of the work on lonely rural interstates, rather than in dense urban centers, where battery powered vehicles (some with pantographs and some without) could ply existing city streets. I suspect that a demonstration project adapting the FREX bus that goes from Colorado Springs to Downtown Denver, and electrifying the part of its route that goes on interstate highways, could probably be put in place for $25 million ($5 million for the buses, $20 million for the overhead catenary and fleet charging infrastructure), which is a small fraction of the cost of any type of electrically powered passenger rail system.
This kind of system would also be more robust than a traditional rail system. For example, if an accident or debris or a sinkhole or construction obstructed the area under the overhead catenary at some point, pantograph powered vehicles could simply detach for a few miles to detour around the problem area, while running on battery power, and then reattach to the wires down the road. This flexibility would also make the system a less attractive target to terrorists, because simply disrupting the wires at a single point could not bring the system to a halt the way destruction of train rails could.
The system could start with pantograph equipped buses, and could latter be expanded to include other pantograph equipped vehicles. The pantographs used to power vehicles on highways could also be used to recharge the vehicle in their home garages -- keeping high voltage connections above the level where people would be prone to accidentally making contact with them.
Why bother doing this at all? The main reason is the rising price of oil. Oil prices are expected to increase far more than electricity prices in the next many decades. We also have more mature technologies make the electrical power grid greener, by replacing high pollution coal powered plants with less polluting power plants that use renewable or nuclear sources, than we do technologies that allow internal combustion driven vehicles to be less polluting.
This low tech solution is also a much more plausible candidate for countries like China and India that are likely to see a huge rise in the number of vehicles operating on their roads, that aren't ready to pay the big bucks that an affluent country like Japan or France can afford to spend on expensive new high speed rail systems.