The driver/owner might like the OP’s method (federal method). If it happens to be in a low cost of gas state, the driver will make money. I think most agree to split the actual costs, but I don’t think offering a flat fee is out of line.
I think the fairer thing to do is to use # of miles as calculation. My company pays me $.5/mile. When it comes to car, it is more than just the gas money, there is insurance, cost of the car, etc. When people only chip in for gas (and split it evenly with the car owner), they are paying for a small fraction of cost.
But if the driver was going to drive home anyway, anything is gravy. Do you really expect to be reimbursed for wear and tear on the car? I wouldn’t.
This is driving with a friend not acting as Uber.
When D1 used to drive back and forth to school, the cost of gas for one way was around $20 (~200 miles). Every once in a while a friend would ask her for a ride. I would tell her why bother to collect $10 from a friend, just do it as a favor. More often than not, they would just pay for a meal for her.
I didn’t really let her drive strangers home.
@doschicos 800 miles
It’s probably just easier if the one receiving the ride pays for a full tank of gas when they stop to fill up. If it’s a long drive and they stop multiple times, then cover every other tank. If there’s multiple passengers then they can take turns, or everybody just give $xx to the owner of the car.
It would also be a nice gesture to pick up lunch for the car’s owner if they stop, assuming it’s simple fast road trip food. Personally in a situation like this I err on the side of being generous vs figuring out an exact split. Assuming they’re riding with a friend; if it’s a total stranger then yes, maybe an exact calculation is better.
That’s what I’d tell my D as a general guideline on etiquette, then I’d let her figure out the rest. Kids these days have their own ideas on how to handle things, all we can do is make suggestions.
@anomander It’s all Venmo now, no cash ever changes hands.
I agree, I want her to err on the side of generosity because the plane ride home for autumn break was a nightmare.
Thank you all. It sounds like gas money and lunch is fair compensation.
It’s nice she’ll have a friend as a companion and someone to share the drive. Road trips with friends can be fun. 
My D occasionally got rides down from school (about 325 one way). I told her to give the kid driving $50. Some people might think that was a lot, but it was less than the bus or train and, certainly, less than a plane. It guaranteed that she was offered a spot in the car first. She was dropped in a park about a 10 minute drive from us so the driver could just get on and off the expressway easily. It worked very well.
My sons both have had/have cars at college. One was far from home, and I know he gave a guys who lives close to us a ride at least once. They worked out cost. I would have been fine with nothing.
My other son has two roommates, and he gets the 1 free parking sticker. So he is the designated driver for things like grocery trips. He occasionally drives a roommate who lives near us home, but I don’t think he’s ever accepted money. Now a second kid has a car, and we (I) pay that student’s share of internet, which works out to be about the same as suing for half of his parking space.
As long as everyone feels ok, it’s all good.
“I think the fairer thing to do is to use # of miles as calculation. My company pays me $.5/mile. When it comes to car, it is more than just the gas money, there is insurance, cost of the car, etc. When people only chip in for gas (and split it evenly with the car owner), they are paying for a small fraction of cost.”
Fixed vs variable costs.
I actually think that the federal reimbursement rate per mile, divided by the # of riders, is the fairest thing. (I was oblivious to this as a college student, when fixed costs/wear and tear did not enter my mind.) I would suggest to your student that s/he suggest it to everyone upfront.
Pimpy idea. I’d tell you to screw off. It’s a fixed cost because it will happen even if you parked the car in the garage. Good way to have no friends.
The idea of charging per mile just gives me a bad impression. If I was driving 800 miles to get home I would have to do that whether or not I had someone coming along with me. If I had a friend also joining for the ride I would take that as company and a benefit to me as having another person to help so that I don’t have to drive all the way by myself. I wouldn’t think to charge anyone but it would be nice if they offered to help pay for gas and toll and that too I would take it as a generous gesture. The space is available in the car anyway so how am I being inconvenienced if someone is sitting next to me.
Charging per mile sounds more like a business transaction. You do that when you take uber or a taxi or when you are getting reimbursed by the company for a business trip and this is amongst friends. In this scenario I think it would be best for the students to decide on their own and the decision would be more casual. (If you are willing to give me a ride I would like to offer you half the costs for toll and gas) Sorry but charging per mile sounds like the driver is trying to profit from having a friend in the car for a trip they were making anyway.
College students often give rides to people who are not necessary friends, so it could be more of a business transaction.
It could be but in this case the OP stated in her first post that it is a friend.
“My youngest will be riding home with a friend for winter break.”
My son and his friends took a long car trip this summer. The car was a leased car from one of the student’s parents. They split the operating cost 3 ways (hotel, gas, food) for everything. When one had to fly back because college stared early, they split the cost 2 ways for the return. The lease payment and insurance on the car they used would have to be paid regardless of whether it sat or was use.
If the car is owned and paid for by the student and not provided to them by a parent, or if the family is not in the best financial circumstances, I suggest your student cover all of the gas. Each can cover their own food, and they can split any lodging. That engender more good feelings and encourage them to give your student a ride next time.
When S took a longer car ride with a friend, he paid for all the gas. The other kid (or his parents) were paying all the other expenses related to owning/operating the car. An 800 mile trip might take about $80 in gas. S would just charge the gas to our card. We were grateful to save on the air fare. We also told S to charge a meal or two for both along the way. Like @TooOld4School said, you may want a ride again.
My kid drove people to and from college 5-6 hours away without charging anything. She was going to drive anyway, and preferred the company.
When I was in college, driving a big 8 miles to the gallon car, the actual round trip cost in gas, tolls and other “essential fluids” to drive between Boston and New York for the was about $75. I would charge 4 other people $15 per head per direction door-to-door service. I made no bones about doing this for a little profit, and I had no problem filling my car both directions.
My point is that I can make the argument for either case depending on the financial circumstances of those involved.
@ClassicRockerDad I wouldn’t have thought to charge anything in this scenario. Honestly sometimes you just do things out of the kindness of your heart or just to help somebody but I guess that is not very common these days. It’s the holiday spirit.
I have a college about 1/2 hour from me. I am part of that facebook group. Lots of parents from out of town are concerned for their kids because they are so far away that the parents can’t drive at a moments notice if their child needs help. I have offered to pick up prescriptions or pick up a cake and balloons for a birthday for out of town parents. Sometimes parents will say my child is lonely or hasn’t made friends yet. I offer to take their child to do some errands. (grocery trip, Target run, whatever they need) My daughter will meet them for lunch sometimes just to check in on them and make sure they are ok. At times the students have offered to pay but I say there is no need. It was my pleasure. Someone needed a ride to the airport so we picked them up from school and we took them. No big deal. We all just try our best to help one another.