Imagine a bus built with carbon-dioxide-based composite materials and coated with a material that can produce clean air as it glides quietly down the street.

That bus, for now, is parked in a virtual world created by Gabriel Wartofsky, a student at the Art Center College of Design in Pasadena, Calif. Wartofsky, along with two fellow students, designed what they envision public buses will look like in 2050 for a competition held by the city of Santa Monica, next to Los Angeles.

"I set out to design a bus that transforms the currently pleasant and convenient ridership experience into a desirable daily occasion," wrote Wartofsky on a blog maintained by him and other designers.

Santa Monica unveiled the three winning designs at the AltCar Expo and Conference last week.

The designs are only concepts, for now. They students haven't mapped out the science behind the vehicles or built models or prototypes.

But the city plans to pitch the ideas to bus makers and public transit officials at the annual American Public Transportation Association conference in October, which will showcase vehicles such as a hybrid-electric bus from Proterra that can run on fuel cells or batteries. The city also intends to approach California state lawmakers about getting research and development money to make at least some elements of designs a reality sooner than 2050.

Encouraging more people to use public transit is good thing. Riding buses, rail and other modes of public transportation saves 1.4 billion gallons of gasoline in the United States per year, according to the transportation association.

But the greentech world doesn't pay as much attention to environmentally friendly buses than low- or zero-emission passenger cars and trucks. The public transportation industry is heavily regulated and can take years to embrace new technologies, and the market is smaller than that of passenger vehicles.

Still, more public transit agencies are favoring buses using alternative fuels or built with hybrid engines, USA Today reported. They can make good test vehicles for early-stage technologies as they have public exposure, drive many miles and are larger than passenger cars, allowing more room for things like hydrogen storage.

And they have inspired Pasadena college students to come up with designs that represent a dramatic departure from the buses of today.

Wartofsky's "Icon Bus," for example, has "gills" alongside the double-decker bus that are coated with titanium oxide, which can break down harmful ozone and release oxygen to create cleaner air inside and outside of the vehicle. Titanium-dioxide air filters already are sold for use in homes and cars.

The "Icon Bus" also features electric motors fed by lithium-ion batteries and roof-mounted solar cells to power lighting and control temperature and other on-board settings.

To regulate the air quality and temperature inside the bus, Wartofsky envisions rooftop panels that can change from white to black to absorb or reflect the sun's heat. A system, modeled the one in use at Japan's Kansai Airport, would circulate filtered air.

Finally, the vehicle's shell would consist of composite materials made from carbon dioxide captured from the atmosphere.

Another winning concept was the "Cougar Bus" designed by Giuseppe Fillippone, which would reconfigure itself to meet various ridership needs.

The imaginary bus would mechanically separate its passenger cabin from its chassis and mainframe, making it possible to use a larger passenger cabin during busy commuter hours and a smaller one at other times.

Fillippone posted three-dimensional computer drawings of how this would work on a blog that also features the two other winning designers and discussions about the inspirations behind various elements of their designs.

In the third design, by Mike Peterson, the "Clear Volume Bus" would run on hydrogen fuel cells, with energy-storage packs running along the walls and roof of the bus.

The bus also features radio frequency identification technology (RFID), which would allow riders to wave their ID cards in front of a card reader and get billed later. Peterson also put in both conventional seating and more space-saving vertical chairs that riders would lean into – but that he claims would still be comfortable.

At this point, it's unclear if any of these buses would be commercially viable. But if these ideas end up inspiring bus makers and are cost-effective enough to materialize on real streets, we might one day have the chance to try out those seats for ourselves.