The original field of 136 experimental vehicles vying for a $10 million prize in Progressive Insurance's Automotive X PRIZE competition has been whittled down to just nine finalists, competition organizers said Tuesday. Each of these finalists, having passed on-track testing at Michigan International Speedway, now move onto the validation phase, where the vehicles must prove they can exceed 100 MPGe, which stands for "miles per gallon energy equivalent."

The field of nine includes:

Mainstream Class (Two vehicles, one team)

•    Edison2, Very Light Car #97 (Charlottesville, VA), Internal Combustion Engine

•    Edison2, Very Light Car #98 (Charlottesville, VA), Internal Combustion Engine

Alternative Class – Tandem (Two vehicles, one team)

•    X-Tracer, E-Tracer #72 (Switzerland), Battery Electric

•    X-Tracer, E-Tracer #79 (Switzerland), Battery Electric

Alternative Class – Side-by-Side (Five vehicles, five teams)

•    Aptera, Aptera 2e (San Diego, CA), Battery Electric

•    Li-ion Motors, Wave II (North Carolina), Battery Electric

•    RaceAbout Association, RaceAbout (Finland), Battery Electric

•    TW4XP, TW4XP (Germany), Battery Electric

•    ZAP, Alias (Santa Rosa, CA), Battery Electric

The competition centers on fuel efficiency. "MPGe is a measure of how much energy is put into a vehicle against how far it will travel using that energy," says X PRIZE Foundation CEO Peter Diamandis. Whereas competition organizers stayed out of how the competitors approached the problem, each team did need to be able to fuel their vehicle using the existing infrastructure. This meant that gas, biofuels and electricity were fair game but hydrogen was off limits.

The vehicles are broken down into three classes: mainstream, alternative tandem and alternative side-by-side. At an awards ceremony on September 16 in Washington, D.C., the winner of the mainstream class will receive $5 million, whereas $2.5 million will go to each of the two alternative vehicle classes.

During the validation phase, all vehicles undergo dynamometer simulated road testing under controlled laboratory conditions at Argonne National Laboratory facilities in Illinois. The car in each class that exceeds 100 MPGe, meets the emissions and performance requirements, and, in the case of a tie, completes a combined performance and efficiency challenge with the fastest time, will win.

Many of the competitors have been startup ventures looking to prove a concept and perhaps catch the eye of bigger players in the auto industry. The Aptera team, for example, is pushing to create a production model of its all-electric 2e vehicle within the next year. Aptera, which has received investments from IdeaLab and Google, is competing in the alternative side-by-side class, which means the design allows the driver and passenger to be seated next to one another in a small cockpit.

Image courtesy of the X PRIZE Foundation