I think the taxi looks the same too. It'd be much easier to be able to communicate with your driver and be like "HEY! STAY WITH US!" haha.
The one where they look more nervous looks like it's near an entrance to the freeway (from the sign in the back) so might be earlier in the race? Although from McCarran they wouldn't need to be on the freeway at all. The closest that they would be to the freeway would be when they're in the south end...near MGM, Mandalay, Monte Carlo, etc. as they would be on Tropicana. IIRC correctly there are NO signs on LV Blvd directing you to the freeway until you hit right by New York New York.