I'm going to ask my passengers to split the whole cost of gas money from a long road trip
What if they refuse to pay anything?
I'll kick them out of the car.
It's always appropriate for passengers to help pay for gas, and not unreasonable for a driver to ask for it. However, you can't expect people to have cash at a moment's notice, so don't kick them out.
Oh wow, what a nice guy. I was joking, I wouldn't really kick them out of the car.
Okay, but you should ask them for the money in advance, ideally before agreeing to go on the trip.