How Stackable Cars Will Work

In designing the City Car, the MIT Media Lab Smart Cities group set out to create a vehicle that wasn't the continuation of old designs, but rather a drastic rethinking of what city residents need from an automobile.

For many, public transportation and private automobile usage have long been mutually exclusive choices. Car-sharing programs that allow multiple individuals to share short-term use of a vehicle have changed this. Say you wanted to travel to a destination a few miles from the nearest train station. A car-sharing program would allow you to rent a vehicle at the station to complete your journey.

Existing car-sharing programs allow members to borrow a vehicle, use it, and then return it to its original location. Bicycle-sharing programs, however, typically allow residents to obtain a bicycle from one location, ride it to their destination, and leave the bike at a nearby drop-off point. The City Car design follows this second model, setting out to create a vehicle that can be checked out at one location (ideally near public transportation stations and major attractions) and returned at another. The vehicles wouldn't replace busses and trains, just fill in their geographic and logistic gaps.

Currently, designs call for the City Car's lightweight body to boast a folding axis and a simple pivoting mechanism to fold the vehicle into a vertical position. The lightweight cars would weigh about 1,000 to 1,200 pounds (454 to 544 kilograms) [source: Lombardi]. The vehicle could then be locked into place directly behind another City Car. These racks would be connected to the city's power grid, allowing stored cars to charge their lithium-ion batteries. Ideally, a vehicle would be fully charged by the time it cycles through to the front of the stack.

But where does the engine go? Amazingly, the design calls for the car's body to house only computer systems and a power source. The City Car's motor, suspension and even its steering are all located within its high-tech wheels.

If you look at a typical automobile, you'll notice that the engine, suspension system, axles and steering column take up a great deal of space. Creating a smaller car means either creating smaller versions of these components or creating new mechanisms that provide the same functions. The team of designers at MIT Media Lab Smart Cities group chose to solve this problem by putting the responsibility of all of these components into what they call robot wheels.

Small Car Image Gallery

Each of the vehicle's four wheel assemblies is a self-contained mobile unit, supplying its own motor, suspension, brakes and steering. Each robot wheel has only two outside needs: electricity (supplied by the car's battery) and digital data to tell the wheels what to do. In a traditional car, the steering wheel physically turns a steering gear, which in turn directs the front wheels in the chosen direction. The City Car, however, will use a drive-by-wire system. The steering wheel won't physically turn anything -- it'll just send the information to the self-steering wheel assemblies.

The robot wheels implement two particularly innovative technologies.

The robot wheels would work in unison, allowing the car to rotate 360 degrees [source: Mack]. This provides an incredible degree of maneuverability, such as allowing drivers to parallel park by simply driving sideways.

There's more to the City Car than amazing wheels and a folding axis. On the next page, we'll look at the ways in which its designers hope to protect drivers, allow customization and even enable vehicles to talk to one another.

You've just arrived at a train station and need to drive several blocks to a job interview in the city's financial district. You swipe your credit card at a City Car rack, wait for the front car to unfold, climb aboard the vehicle and enter your destination in the car's computer. A warning message flashes across the screen to tell you that other City Cars have encountered delays in that part of town due to road work. The vehicle runs a few computations and suggests an alternate route.

This is just one example of how the City Car's onboard computer, driver interface and inter-vehicle communication system may one day help make drivers' lives a little easier. With access to the latest maps and traffic information (similar to a GPS system) and constantly updated information from other City Cars, the vehicle's computer system could be the equivalent of riding with a veteran taxi driver.

This technology could also play a role in protecting the driver from harm. The vehicle could keep track of other City Cars and prevent accidents by warning if one vehicle's coordinates come too close to another's. The City Car design team also hopes to implement other groundbreaking safety features, such as soft, robotic "fingers" that fold up from the sides of seats to clutch drivers in the event of an accident. Revolutionary "liquid" materials may also play a crucial role. These materials would allow the cabin to change from a hard structure to a soft, shock-absorbent consistency upon impact during an accident. For more information on this technology, read How Liquid Body Armor Works.

From clever bumper stickers to custom vinyl, vehicle owners put a great deal of personality into their cars. While the idea of shared cars may seem like the complete opposite of individuality on the road, City Car designers hope to allow drivers to express themselves in a very unique way. The City Car design may implement a technology that allows you to change the vehicle's color scheme at the push of a button. Thin, programmable displays would cover both the exterior and interior of the vehicle, making many of the car's aesthetic qualities as customizable as a computer desktop.

And this means more than just decking out a City Car in your favorite sports team's colors. All the gauges and dials in the vehicle's cab would run on the same technology, allowing users to adjust dashboard displays to meet their needs and tastes. Additionally, City Car's various traffic signals would no longer be limited by bulb placements, but could incorporate the entire vehicle. Imagine if hitting your emergency lights caused your whole vehicle to flash red, or if a right-hand turn signal lit up the entire passenger side.

The City Car represents a possible shift in the relationship between cars and humans, from a commodity you own to a resource you share with the rest of the population. To explore even more concept car designs, follow the links on the next page.