Does interstate speed limit apply to instantaneous car velocity or to average car velocity for the whole trip?
Instantaneous. All posted speed limits generally apply to instantaneous speeds, and it’s not possible for your average speed to exceed the speed limit unless your instantaneous speed exceeded the speed limit at least some of the time. However, there are times that you can get a ticket based on your average speed. For example, sometimes you get on a toll road and you get a receipt that tells where you are and the time. When you exit, they take your receipt, calculate how far you went and charge money based on that. Well, they have your start time, your end time and the distance, and can figure your average speed.
