Ethics is two things. First, ethics refers to well-founded standards of right and wrong that prescribe what humans ought to do, usually in terms of rights, obligations, benefits to society, fairness, or specific virtues.
If you mean the average speed limit, it's probably 65 MPH. In 1995 Congress repealed the national speed limit of 55 and it is now up to states again to determine the limits. About 30 states have limits of 70 MPH or higher. A few Western states have no speed limits on certain stretches of highway.
30 mph UK speed limit. The 30 mph UK speed limit (48 km/h) is also used in residential areas and is the most frequently used within villages, towns and cities. The vast majority of UK roads within urban areas are 30 mph. Unless signs suggest otherwise, UK roads with street lighting will almost always have a speed limit of 30 mph.