greydius corrected me asserting that the factor between ligth speed and car speed is 10 millions, and not one million as I said.

But in true there are production cars that pass 430 km/h, resulting in a factor of about 2.5 millions. A lot less than 10 millions.

https://en.wikipedia.org/wiki/Production_car_speed_record

You should not compare the fastest car speed, but the average car speed, which for this argument would probably be closer to 200km/h. That puts it in a factor of 5 million, which is within one order of magnitude of the original guess.