Ground Cover As Parking Surface

I read your ground cover as lawn replacement article. But I am hoping for something really low growing and on the economic side, can be planted from seeds. Do you have any recommendations for something that grows even shorter than the thyme you discussed in the article and would be tough enough to handle our car parked on it? We are in Seattle, Washington, USA - so USDA says zone 7B?

Rupturewort might be your best bet for a tough very low growing ground cover.
But do consider the much more attractive option of using paving stones in the tire tracks and establishing minus thyme in the rest of the driveway and between the cracks. Make sure the cracks are one to two inches (two to five centimeters) wide with the soil/sand level half an inch to an inch (one to two centimeters) below the level of the paving stone tops. The thyme is available in economical plug trays and planting the plugs six inches to one foot (15-30cm) apart will mean one season of weeding and then the bliss of a tight ultra-low carpet.