High school and college students from across North America are in Houston for the annual Shell Eco-marathon, where teams compete to see who can build the most fuel-efficient vehicle.

Among the 70 teams this year are six girls dubbed the “ShopGirls” of Granite Falls High School in Granite Falls, Wash.

Their squat, one-person car is the same one their school entered last year, with upgrades.

“We moved things, like the mirrors used to be on the outside of our car,” says senior and team manager Shante Stowell. “By putting them on the inside of our car, that makes us more aerodynamic.”

The team also added covers to the bicycle wheels.

“When bike wheels travel through the air, they cut up the air and you lose a lot of aerodynamics,” Stowell says. “If you cover the spokes, they don’t do that as much.”

The car is powered by a 250cc, 4.5 horsepower, air-cooled diesel engine. It is small and needs a fuel tank that is about the size of a soda can.

“It’s 250 milliliters, and on one tank of gas we can go around 35 miles,” says sophomore Pooja Sethi.

“Last year we got 470 miles per gallon, and this year we want to break the record and get 678 miles per gallon. That’s our goal,” she says.

Granite Falls High School manufacturing instructor Michael Werner oversees the team. He says the previous diesel record was 563.3 mpg, set in 2009 by students at College of the Redwoods in Eureka, Calif. The ShopGirls team wants to beat that by at least 100 mpg.

While most of the team’s work since September has been focused on engineering, Stowell says there were aesthetic decisions to be made — such as what color to paint the car.

“We kind of wanted it to be girly, but we didn’t want it to be pink-and-purple-princess-y,” Stowell says. “We decided we wanted it to be hot pink, and the color that goes with hot pink the best is lime green.”

The current global record holder for the Shell Eco-marathon challenge is the Polyjoule team from Polytech Nantes University in France. In 2010, their fuel cell-powered vehicle achieved the equivalent of 11,516.34 mpg. Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.