My family has the philosophy of "you only need one less car than the amount of drivers in a family." This makes sense for families that don't always have drivers in the house, like mine. In my family, my dad, sister, and I drive, and not my mom. This means that when I am home from college, my sister and I share a car, and that was only after she graduated college and came home to work. Before that, all three of us had to fight for the keys to my dad's car. We didn't have the luxury of driving to high school when we were younger, even though we've had our driver's licenses since. So when I come home, there's always an amount of struggle for logistics when all three of us need a car to go places. The main points to win a car for the time of day would be dependent on: importance, time, and distance. Otherwise, I need to find a ride.
If I want to take a car for a certain amount of time, it needs to be for a good reason. I have to be going somewhere where I can't get a ride. The main things I get a car for would be for religious activities. If it is school involved, aside from extracurricular activities, I have to have some reason why I couldn't get a ride earlier on before figuring out who can give up their car for me. However, a lot of times, especially when I'm home on break, I will use the excuse that my mom needs to go somewhere to shop, usually for groceries. However, most if not all the time, it backfires and I end up chauffeuring my mom around all day to different stores. There are some cases where I need to use a car for its utility. My dad has an SUV, so if I needed to transport something big, I would need to take my dad's car. Otherwise, I most likely have to duke it out with my sister for our car.
My dad and sister work, so they of course need transportation to their respective occupations. So if, during the workweek, I need a car, I have to make sure that I drop off and pick up whoever's car I'm for that day, assuming I get said car. However, during the weekend, I have to debate with the other two to see who needs a car for said times, especially since we all want to go do things with our friends. I can't exactly debate taking a car from my dad to go hang out with friends, so I usually have to figure things out logistically with my sister. She understands that I can't always ask for a ride from them, so we try to schedule things between each other. That being said, when we both have plans at the same time, importance and distance come into play.
If I need a car to go back to campus (Virginia Commonwealth University) for a certain amount of time, usually for the weekend, I have to make sure that one of the two cars is free, which is usually a rare occasion. However, when I need to go further than a half hour away to be somewhere, if important enough, I will usually be able to take a car compared to somewhere within a half hour. In that case, I usually get a ride to and from, or I have to get dropped off by someone and find my way back.
As you can tell, the three categories work in tandem with each other, making things even more complicated. However, you can't exactly figure out one without bringing up the other. Most of the time I figure things out with my sister, but there are definitely times where all three of us need a car. Usually, whoever doesn't have as important of a need will either be dropped off by the others or will find a ride. Then after that, whoever needs to travel further distance will take the more fuel efficient car, or whoever needs the SUV for utility will take the SUV, even if they need to go further distance. Then depending on time, whoever is free more during the day has to either pick up the stranded (meaning without a car) person or tend to my mom's needs to go places. All in all, having a car for each of us drivers would be ideal, but we're not there yet financially, so we make the two cars for the three of us work.