The time has arrived for practical, 100-mile-per-gallon cars that can be built on a budget of about $10,000, said designers of those vehicles. A trio of prototype vehicles will cross the heartland of America Aug. 15-20 in Rally Green, a long distance fuel economy rally/demonstration for high-mileage vehicles. The 2,200-mile rally will be a road test for these do-it-yourself designed cars built to attain 100 miles per gallon.

Entrants Jack McCornack and Jay Perdue are noted inventors whose alternative transportation pursuits have been followed by the Discovery Channel, Mother Earth News, Wired, the New York Times and other media.

The third entrant is Rally Green organizer Bill Buchholz of the Camden area. He is a wooden boat builder and creative thinker who wanted to position homebuilt high-mileage, practical and good-looking cars at the forefront of the public eye.

Rally Green does that with a schedule spanning 2,200 miles in six days across seven states, an ambitious average of 350 miles per day. The green flag dropped Aug. 15 in Knoxville, Iowa, and the fleet plans to cross the Golden Gate Bridge Friday, Aug. 20.

The course tests endurance along some truck-heavy interstates, mountain passes and desolate desert.

The entrant roster has settled out to three, including Buchholz fellow Maine Automotive X Team entry Dirigo, a homebuilt front-wheel-drive tadpole trike powered with a three-cylinder diesel. Buchholz and team have crafted eco-friendly cars with the thought that consumers could use them 80 percent of the time on their everyday errands.

Dirigo’s transmission is five-speed manual, from a 1986 Ford Ranger pickup. The body — and this is where Buchholz’s boat building craftsmanship is evident — is a single layer of quarter-inch western red cedar sheathed both sides with fiberglass. Fenders and air dam are carbon fiber. The best fuel mileage to date was 99 mpg, with closer to 75 mpg averaged at highway speeds. As a commuter car, the two-passenger Dirigo boasts plenty of legroom. Buchholz even made a Naugahyde cup holder.

“During rest stops along the Rally Green route, we hope to engage all kinds of people in a conversation about fuel economy and sustainable transportation,” said Buchholz. “I think we have such an amazing group of characters driving such fabulous cars that the country will be listening.”

McCornack’s MAX is a multi-fuel sports car built for Mother Earth News. It runs on diesel, biodiesel or straight vegetable oil — all of which will be employed during the course of Rally Green’s 100-mile-per-gallon goal.

Perdue’s Tri-Hybrid Stealth is a tandem trike whose rear wheel is mobilized by three power sources: diesel fuel, electricity and human exertion. The option of human pedal-power is for exercise (Perdue is a health enthusiast), but it also helps charge the 46 lithium ion phosphate batteries even while the driver is sitting at a red light. The name alludes to the car’s black, flat-panel appearance that recalls the U.S. Air Force’s Stealth fighter jet.

Rally Green is an offshoot of a 100-mile trial last summer in New England called the One-Gallon Challenge. Dirigo was originally built to compete in the Progressive Automotive X Prize, a contest of 100-mpg designs for mass-production, Buchholz said.

Rally Green is not the first test of home-built prototype cars, but it may be the longest-distance test of high-mileage achievement for this variety of vehicles, Buchholz said.

Visit dirigocar.com for course maps, links to entrants Web sites and more.