In the first few hours at Michigan International Speedway, I saw many triumphs. Teams approached the tests and quickly conquered them, moving on to the next challenge. The core three tests we were conducting had been passed in the previous phase, except by a few international teams waylaid by the Iceland volcano, thereby steepening the learning curve. But most just shrugged it off and made it happen.

The skidpad test was new for all, but this proved straightforward (even though they were driving in circles!) for most contestants. The goal is to simply follow the 300-ft circle as fast as the car will hold the line, aiming for .7 lateral g or higher. With its serious lean, the Swiss E-Tracer was exciting to watch, and a Western Washington University driver got a wake-up call from their rear-drive car before learning how to hold the line.

But as the hours passed, a few teams began having struggles and the reality of being bumped from the competition began to become more apparent. Later in the day at the acceleration course, we saw Amp, Illuminati Motor Works, and TW4XP all see their hopes threatened. Each team is allotted 10 attempts at this test, spread across two time periods.

As the failed runs began adding up, each team eventually took a break to strategize and even tweak the cars. Amp, with a well-finished Saturn Sky, returned with tape over the front end to improve aerodynamics, but it wasn’t enough to overcome an apparent mechanical problem with the car. It would later pass this vital test and continue on in the contest, but it is a close call.

The large, four-door Illuminati car had been a pleasant surprise in previous tests, but an apparent transmission problem frustrated the team and its efforts to make the run quickly enough. Watching the radar gun, each 0-60 mph run had perfect portions, but a shift compromised the acceleration time. Add together the best portions of the runs, and the silver sedan would have likely made it.

The small, two-seat TW4XP spent its final minutes being reprogrammed from a laptop for one last run, but the adjustments couldn’t push the car below the 20-second cut off time. However, Tuesday morning they were able to pass the test, after the batteries were fully charged.

Teams who have failed a test have an opportunity to appeal to the X Prize technical staff, so the final judgments aren’t set in stone until the official standings are updated. But it is clear that there will be fewer teams proceeding Tuesday. And notably, Illuminati Motor Works was one of two teams remaining in the Mainstream class. The other team, Edison2, is going strong, but to win, they will need to continue to pass each remaining test.

It is sad to see so many creative, dedicated, and talented teams reach the end of the X Prize road. Many have made serious sacrifices to accomplish what they have, and all deserve our collective admiration.

Finally, to me it’s clear that this competition shows how hard it is to create a viable car of the future-- especially on a tight schedule and without the vast resources of a major automaker. But many teams continue, showing there is hope that a green machine of tomorrow may far exceed the fuel economy of today’s mainstream, production vehicles.

To track your favorite team, check out the Automotive X Prize twitter feed or watch live video from the X Prize website.

Follow our Auto X Prize coverage here in the Cars blog, as well as in our special Auto X Prize section and via Twitter @CRcars.

–Jeff Bartlett