It really depends on the circle of people that are at parties in the US. I've been the DD and have been at parties where there is at least one DD. I think there was a general consensus not to bother or pressure the guy DDing. All the fraternities and sororities would have a DD system running on fridays and saturday nights for their members as well, this is typical for a lot of universities but it only covers those members and their friends. I've also been at parties where I know there was no one DDing and I knew pretty much everyone drove there and didn't spend the night. Thankfully I lived in the college town with a decent bus system that got us around to most of the area for free so even if I couldn't get a ride, I could use the bus. I also purposely moved downtown just to have a ability to get almost anywhere without a car. The bus system was nice but getting between certain areas of town was hard depending on where you lived.